Framework wide color (#54415)

issue: flutter/flutter#127855
integration test: #54415

This does the preliminary work for implementing wide gamut colors in the
Flutter framework. Here are the following changes:
1) colors now specify a colorspace with which they are to be interpreted
1) colors now store their components as floats to accommodate bit depths
more than 8

The storage of this Color class is weird with float/int storage but that
is a temporary solution to support a smooth transition. Here is the plan
for landing this:
1) Land this PR
1) Wait for it to roll into the Framework
1) Land flutter/flutter#153938 which will make
CupertinoDynamicColor implement Color
1) Land another engine PR that rips out the int storage:
#54714

Here are follow up PRs:
1) #54473 - changes DlColor so the
wide gamut colors are rendered
1) #54567 - Hooks up these changes
to take advantage of wide DlColor
1) flutter/flutter#153319 - the integration test
for the framework repo

There are some things that have been left as follow up PRs since they
are technically breaking:
1) The math on `lerp` hasn't been updated to take advantage of the
higher bit depth
1) `operator==` hasn't been updated to take advantage of the higher bit
depth
1) `hashCode` hasn't been updated to take advantage of the higher bit
depth
1) `alphaBlend` hasn't been updated to take advantage of the higher bit
depth
1) `toString` hasn't been updated to take advantage of the higher bit
depth

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or the PR is [test-exempt]. See [testing the engine] for
instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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Author: gaaclarke

lib/gpu/lib/src/render_pass.dart

@@ -95,6 +95,15 @@ base class RenderTarget {
   final DepthStencilAttachment? depthStencilAttachment;
 }
 
+// TODO(gaaclarke): Refactor this to support wide gamut colors.
+int _colorToInt(ui.Color color) {
+  assert(color.colorSpace == ui.ColorSpace.sRGB);
+  return ((color.a * 255.0).round() << 24) |
+      ((color.r * 255.0).round() << 16) |
+      ((color.g * 255.0).round() << 8) |
+      ((color.b * 255.0).round() << 0);
+}
+
 base class RenderPass extends NativeFieldWrapperClass1 {
   /// Creates a new RenderPass.
   RenderPass._(CommandBuffer commandBuffer, RenderTarget renderTarget) {
@@ -105,7 +114,7 @@ base class RenderPass extends NativeFieldWrapperClass1 {
           index,
           color.loadAction.index,
           color.storeAction.index,
-          color.clearValue.value,
+          _colorToInt(color.clearValue),
           color.texture,
           color.resolveTexture);
       if (error != null) {

lib/ui/lerp.dart

@@ -26,7 +26,7 @@ double? lerpDouble(num? a, num? b, double t) {
 ///
 /// Same as [lerpDouble] but specialized for non-null `double` type.
 double _lerpDouble(double a, double b, double t) {
-  return a * (1.0 - t) + b * t;
+  return a + (b - a) * t;
 }
 
 /// Linearly interpolate between two integers.