[browser][coreCLR] TypeScript host skeleton

[pavelsavara]

TypeScript + RolllupJS

Goal of this PR is to replace previously merged generated .js with the TS source and necessary compiler+bundler tooling.
Another goal is to produce minified and mangled (small) Release versions of said files.
This is mangled + beautified version of Rollup output from this PR

Rollup

• minificable cross JS module exchange of functions - cross-module.ts
• minificable sharing of JS symbols across emscripten libraries - cross-linked.ts
• dotnetUpdateModuleInternals + dotnetTabulateXXX/expandXXX allow the modules to exchange functions on known index in an array, rather than by symbol name. That makes it possible to JS mangle the symbol.
• we want to have some symbols same across all modules, they are in reserved const of rollup.config.defines.js

Emscripten linker

• Emscripten linker executes (our) JS libraries at link time and calls toString on the instantiated functions.
• It's terrible and it breaks closures. It's by Emscripten design.
• To deal with that we can't mangle symbol names that leak out of our closure into emscripten closure
• Symbols that leak into common closure with emscripten have dotnet prefix
• Functions callable from C are also linked this way, they are trimmable by emscripten linker. They have SystemJS_ or SystemInteropJS_ prefix
• in libBrowserHost.footer.js we copy the whole rollup function closure and do take binding at runtime for BrowserHost_ functions callable from C
• in libSystem.Native.Browser.footer.js we install common symbols into emscripten closure from exports.cross

Loader - dotnet.js

• JS host builder + configuration merge
• dotnet.boot.js config loading
• fetchDll -> registerDllBytes -> external_assembly_probe/BrowserHost_ExternalAssemblyProbe
• BrowserHost_ExecuteAssembly -> coreclr_execute_assembly -> BrowserHost_ResolveMain/BrowserHost_RejectMain
• emscripen is responsible for .wasm loading, but we need to change it later so that we handle the fingerprinted name and pre-fetch
• we are missing some Mono features still: re-try, throttling, blazor libraries, progress reporting, ICU loader, load only mode
• host builder is missing: proper exit implementation, unhandled exception registration and some of the internal testing helpers
• logging is missing condition inlining via rollup
• polyfills are simplified to match ecosystem development
• V8 polyfills incomplete: process
• fetchLike polyfill for nodeJS and V8 to work with host file system
• PromiseCompletionSource like TaskCompletionSource but for JS
• runtimeList is registration of the runtime instance into globalThis. There could be multiple dotnet VMs on the same page.

BrowserHost

• public JS API for memory operations, run, exit, env variables
• this part of the host brings non-trimmable JS closure. It's ok because those are public JS APIs and we can't trim them anyway.
• exit implementation is naive, abort registration is missing
• pass host properties like TPA via env variables for now

System.Native.Browser

• implements SystemJS_RandomBytes callable from C and trimmable.
• it will contain Timers, ThreadPool and Finalizer support later

System.Runtime.InteropServices.JavaScript.Native

• contains stub for SystemInteropJS_InvokeJSImportST and will contain more JS interop related C callable function later

dotnet.runtime.js

• is empty at the moment bu will contain JS part of JS interop later
• it could also contain other larger pieces of JS which we don't want in dotnet.js loader or untrimmable parts of dotnet.native.js

Contributes to #119685
Contributes to #113067

[Copilot]

Pull Request Overview

This PR replaces previously generated JavaScript files with TypeScript source code and sets up a complete build toolchain using TypeScript and Rollup. The goal is to produce both readable debug versions and minified release versions of the JavaScript runtime files for the browser CoreCLR host.

Key changes include:

• Complete replacement of hand-written JavaScript with TypeScript source code
• Implementation of Rollup.js-based build system with TypeScript compilation
• Introduction of cross-module symbol sharing system to enable JavaScript minification
• Renaming of C functions and JavaScript functions to use consistent net and BrowserHost_ prefixes

Reviewed Changes

Copilot reviewed 56 out of 58 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/native/tsconfig.json	Updates TypeScript target from ES2018 to ES2020
src/native/rollup.stub.js	Removes temporary stub implementation
src/native/rollup.config.plugins.js	Adds Rollup plugins for minification, source maps, and build optimization
src/native/rollup.config.js	Main Rollup configuration defining all build targets
src/native/rollup.config.defines.js	Defines build constants and reserved symbol names
src/native/package.json	Updates dependencies to newer versions
src/native/libs/Common/JavaScript/*	Implements shared cross-module communication system
src/native/libs/System.Native.Browser/*	TypeScript implementation of native browser functionality
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/*	TypeScript implementation of JS interop layer
src/native/corehost/browserhost/*	TypeScript implementation of browser host and loader
src/native/corehost/browserhost/browserhost.cpp	Renames C functions to use BrowserHost_ prefix

[SingleAccretion]

Some comments on naming and documentation for the cross-module stuff. I am still to go through the Emscripten integration code.

[radekdoulik]

LGTM, besides the other comments.

I think it would be great to document the cross-module concept and also the general library structure somewhere in the docs/. Doesn't need to be in this PR.

[pavelsavara]

/ba-g CI timeout in WBT