Setup webview_flutter_platform_interface package.

Creates a new `webview_flutter_platform_interface` directory and adds
the following meta-data files:
- `AUTHORS`: copied from the `webview_flutter` package and added my name;
- `CHANGELOG.md`: new file adding description for release 1.0.0;
- `LICENSE`: copied from the `webview_flutter` package;
- `README.md`: new file adding the standard platform interface
  description;
- `pubspec.yaml`: new file adding package meta-data for the
  `webview_flutter_platform_interface` package.

Author: mvanbeusekom

packages/webview_flutter/webview_flutter_platform_interface/AUTHORS

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+# Below is a list of people and organizations that have contributed
+# to the Flutter project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.
+The Chromium Authors
+German Saprykin <[email protected]>
+Benjamin Sauer <[email protected]>
+[email protected]
+Ali Bitek <[email protected]>
+Pol Batlló <[email protected]>
+Anatoly Pulyaevskiy
+Hayden Flinner <[email protected]>
+Stefano Rodriguez <[email protected]>
+Salvatore Giordano <[email protected]>
+Brian Armstrong <[email protected]>
+Paul DeMarco <[email protected]>
+Fabricio Nogueira <[email protected]>
+Simon Lightfoot <[email protected]>
+Ashton Thomas <[email protected]>
+Thomas Danner <[email protected]>
+Diego Velásquez <[email protected]>
+Hajime Nakamura <[email protected]>
+Tuyển Vũ Xuân <[email protected]>
+Miguel Ruivo <[email protected]>
+Sarthak Verma <[email protected]>
+Mike Diarmid <[email protected]>
+Invertase <[email protected]>
+Elliot Hesp <[email protected]>
+Vince Varga <[email protected]>
+Aawaz Gyawali <[email protected]>
+EUI Limited <[email protected]>
+Katarina Sheremet <[email protected]>
+Thomas Stockx <[email protected]>
+Sarbagya Dhaubanjar <[email protected]>
+Ozkan Eksi <[email protected]>
+Rishab Nayak <[email protected]>
+ko2ic <[email protected]>
+Jonathan Younger <[email protected]>
+Jose Sanchez <[email protected]>
+Debkanchan Samadder <[email protected]>
+Audrius Karosevicius <[email protected]>
+Lukasz Piliszczuk <[email protected]>
+SoundReply Solutions GmbH <[email protected]>
+Rafal Wachol <[email protected]>
+Pau Picas <[email protected]>
+Christian Weder <[email protected]>
+Alexandru Tuca <[email protected]>
+Christian Weder <[email protected]>
+Rhodes Davis Jr. <[email protected]>
+Luigi Agosti <[email protected]>
+Quentin Le Guennec <[email protected]>
+Koushik Ravikumar <[email protected]>
+Nissim Dsilva <[email protected]>
+Giancarlo Rocha <[email protected]>
+Ryo Miyake <[email protected]>
+Théo Champion <[email protected]>
+Kazuki Yamaguchi <[email protected]>
+Eitan Schwartz <[email protected]>
+Chris Rutkowski <[email protected]>
+Juan Alvarez <[email protected]>
+Aleksandr Yurkovskiy <[email protected]>
+Anton Borries <[email protected]>
+Alex Li <[email protected]>
+Rahul Raj <[email protected]>
+Maurits van Beusekom <[email protected]>

packages/webview_flutter/webview_flutter_platform_interface/CHANGELOG.md

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+## 1.0.0
+
+* Extracted platform interface from `webview_flutter`.

packages/webview_flutter/webview_flutter_platform_interface/LICENSE

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+Copyright 2013 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/webview_flutter/webview_flutter_platform_interface/README.md

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+# webview_flutter_platform_interface
+
+A common platform interface for the [`webview_flutter`][1] plugin.
+
+This interface allows platform-specific implementations of the `webview_flutter`
+plugin, as well as the plugin itself, to ensure they are supporting the
+same interface.
+
+# Usage
+
+To implement a new platform-specific implementation of `webview_flutter`, extend
+[`WebviewPlatform`][2] with an implementation that performs the
+platform-specific behavior, and when you register your plugin, set the default
+`WebviewPlatform` by calling
+`WebviewPlatform.setInstance(MyPlatformWebview())`.
+
+# Note on breaking changes
+
+Strongly prefer non-breaking changes (such as adding a method to the interface)
+over breaking changes for this package.
+
+See https://flutter.dev/go/platform-interface-breaking-changes for a discussion
+on why a less-clean interface is preferable to a breaking change.
+
+[1]: ../webview_flutter
+[2]: lib/webview_flutter_platform_interface.dart

packages/webview_flutter/webview_flutter_platform_interface/pubspec.yaml

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+name: webview_flutter_platform_interface
+description: A common platform interface for the webview_flutter plugin.
+repository: https://github.com/flutter/plugins/tree/master/packages/webview_flutter/webview_flutter_platform_interface
+issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview_flutter%22
+# NOTE: We strongly prefer non-breaking changes, even at the expense of a
+# less-clean API. See https://flutter.dev/go/platform-interface-breaking-changes
+version: 1.0.0
+
+environment:
+  sdk: ">=2.12.0 <3.0.0"
+  flutter: ">=2.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  plugin_platform_interface: ^2.0.0
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  mockito: ^5.0.0
+  pedantic: ^1.10.0