[wasm] icu build related improvements

[radical]

• WasmApp.targets should check that the custom filename starts with icudt_* since it seems to be required.
• When fullIcu==true, then use a nonexistant.dat as the custom filename, so it would catch any cases where we incorrectly use that file (it does)
  

  runtime/src/mono/wasm/Wasm.Build.Tests/IcuShardingTests.cs

  Lines 242 to 244 in 3a88b89

  	buildArgs = buildArgs with { ProjectName = projectName };
  	buildArgs = ExpandBuildArgs(buildArgs, extraProperties: $"<WasmIcuDataFileName>{s_customIcuPath}</WasmIcuDataFileName><WasmIncludeFullIcuData>{fullIcu}</WasmIncludeFullIcuData>");

• Add test for custom file from the runtime pack (context: [wasm] WBT fixes, and rationalization to allow improved testing #89360 (comment))

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

• WasmApp.targets should check that the custom filename starts with icudt_* since it seems to be required

• When fullIcu==true, then use a nonexistant.dat as the custom filename, so it would catch any cases where we incorrectly use that file (it does)
  

  runtime/src/mono/wasm/Wasm.Build.Tests/IcuShardingTests.cs

  Lines 242 to 244 in 3a88b89

  	buildArgs = buildArgs with { ProjectName = projectName };
  	buildArgs = ExpandBuildArgs(buildArgs, extraProperties: $"<WasmIcuDataFileName>{s_customIcuPath}</WasmIcuDataFileName><WasmIncludeFullIcuData>{fullIcu}</WasmIncludeFullIcuData>");

Author:	radical
Assignees:	ilonatommy
Labels:	arch-wasm, area-Build-mono
Milestone:	8.0.0