[browser][CoreCLR] Loading Webcil - JS part

[pavelsavara]

Split of JS part of #124268

• New instantiateWebCILModule() in host assets:
  • instantiates the .wasm wrapper as a WebAssembly module
  • calls getWebcilSize/getWebcilPayload exports to extract the raw WebCIL
  • copies the payload into 16-byte aligned memory, registers it under the .dll virtual path.
• New getWasmMemory / getWasmTable

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
See info in area-owners.md if you want to be subscribed.

[Copilot]

Pull request overview

This PR adds JavaScript support for loading Webcil 1.0 assemblies in the browser/WASM environment, split from the larger PR #124268. The implementation enables CoreCLR on browser to load assemblies packaged in the Webcil format by instantiating .wasm wrapper modules, extracting the raw Webcil payload, and registering it in memory with proper 16-byte alignment.

Changes:

• Added new instantiateWebcilModule() function that instantiates Webcil .wasm wrappers, extracts payloads via exported functions, and registers them under .dll virtual paths
• Exposed getWasmMemory() and getWasmTable() functions to access WebAssembly memory and table from native browser exports
• Updated asset loading logic to detect .wasm assemblies, classify them as "webcil10" behavior, and route them through the new instantiation path
• Replaced hardcoded pointer size constant (4) with exported sizeOfPtr constant for better maintainability
• Removed "WASM-TODO: webCIL" comment as the feature is now implemented

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/native/libs/System.Native.Browser/native/index.ts	Added getWasmMemory/getWasmTable exports to native browser module
src/native/libs/Common/JavaScript/types/public-api.ts	Added "webcil10" asset behavior type
src/native/libs/Common/JavaScript/types/exchange.ts	Added type definitions for getWasmMemory/getWasmTable and instantiateWebcilModule
src/native/libs/Common/JavaScript/types/ems-ambient.ts	Added wasmMemory and wasmTable properties to Emscripten ambient symbols
src/native/libs/Common/JavaScript/per-module/index.ts	Exported sizeOfPtr constant (value 4 for WASM32)
src/native/libs/Common/JavaScript/loader/run.ts	Removed "WASM-TODO: webCIL" comment as feature is implemented
src/native/libs/Common/JavaScript/loader/dotnet.d.ts	Added "webcil10" to public API type definitions
src/native/libs/Common/JavaScript/loader/assets.ts	Added webcil detection in fetchDll, memory promise controller, behavior/content-type mappings, and integration with instantiateWebcilModule
src/native/libs/Common/JavaScript/host/index.ts	Added instantiateWebcilModule to host exports table
src/native/libs/Common/JavaScript/host/host.ts	Replaced hardcoded 4 with sizeOfPtr constant, added .wasm to .dll path mapping
src/native/libs/Common/JavaScript/host/assets.ts	Implemented instantiateWebcilModule with version validation, payload extraction, and 16-byte aligned memory registration; updated instantiateWasm signature
src/native/libs/Common/JavaScript/cross-module/index.ts	Added mapping for new exports in cross-module tables