Copydotnet.d.ts to wwwroot on build/publish.

[ilonatommy]

• WebAssembly builds now expose an opt-in WasmEmitTypeScriptDefinitions MSBuild property (default false) so projects can request the generated dotnet.d.ts typings.
• A new _EnsureDotnetTypeScriptDefinitions target copies dotnet.d.ts from the runtime pack into the project’s wwwroot on build or publish when that property is enabled.
• Added a test (TypeScriptDefinitionsCopiedToWwwrootOnBuild) to cover Debug/Release and verify the file is produced only when requested.

Fixes #77174.

[JakeYallop]

Its also worth pointing that dotnet.d.ts is currently explicitly removed from the build via:

_WasmBuildFilesToRemove:

runtime/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets

Line 279 in 7ab1ed3

<Output TaskParameter="FilesToRemove" ItemName="_WasmBuildFilesToRemove" />

Which is an output from the ComputeWasmBuildAssets task, in that task:

runtime/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/ComputeWasmBuildAssets.cs

Line 93 in 7ab1ed3

if (AssetsComputingHelper.ShouldFilterCandidate(candidate, TimeZoneSupport, InvariantGlobalization, LoadFullICUData, CopySymbols, customIcuCandidateFilename, EnableThreads, EnableDiagnostics, EmitSourceMap, out var reason))

runtime/src/tasks/Microsoft.NET.Sdk.WebAssembly.Pack.Tasks/AssetsComputingHelper.cs

Line 74 in 7ab1ed3

".ts" when fromMonoPackage && fileName == "dotnet.d" => "dotnet type definition is not used by Blazor",

[Copilot]

Pull Request Overview

Adds an opt-in MSBuild property to copy the generated dotnet.d.ts TypeScript definition file into a WebAssembly project's wwwroot during build, addressing issue #77174.

• Introduces WasmEmitTypeScriptDefinitions property (default false) in relevant .targets.
• Adds MSBuild target _EnsureDotnetTypeScriptDefinitions to perform the conditional copy.
• Adds a test validating the file copy on build (Debug/Release).

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/mono/wasm/build/WasmApp.Common.targets	Documents and defines the new WasmEmitTypeScriptDefinitions property.
src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets	Adds property default again and new target to copy dotnet.d.ts into wwwroot.
src/mono/wasm/Wasm.Build.Tests/Templates/WasmTemplateTests.cs	Adds test ensuring dotnet.d.ts is copied on build when the property is enabled.

[ilonatommy]

WBT fail, even though manual run of dotnet build on the WBT project succeeds:
log dotnet.d.ts should be created at /root/helix/work/workitem/e/wbt artifacts/tsdefs_Debug_False_h1qa4fpe_vyr_鿀蜒枛遫䡫煉/wwwroot/dotnet.d.ts after the build with WasmEmitTypeScriptDefinitions=true

[ilonatommy]

@maraf, this one needs more work. While it works when used "manually", WBT fail. I will investigate it when I get time