[wasi+browser] bundle timezones into .wasm

[pavelsavara]

Motivation

• the VFS is slow in the browser. I expect to save 50ms of startup time
• this will bring de-duplication of files with same hash and bit smaller overall download size.
• it will enable memory snapshot of the initialized runtime
• necessary for WASI with <WasmSingleFileBundle>

Changes

• TimeZoneInfo will use this new embedded TZ database for browser and wasi OS
  • unless TZDIR env variable is set
  • if TZDIR is set it would fallback to unix-like file system approach (as before).
• added mono_wasm_get_bundled_file and mono_wasm_add_bundled_file
• mono_wasm_add_bundled_file is called with file names from generated mono_wasm_register_bundle_timezones
• added SystemNative_GetTimeZoneData which calls new mono_wasm_get_bundled_file
• in of <WasmSingleFileBundle> we also generate mono_wasm_register_bundle_assemblies for WASI
• removed dotnet.timezones.blat from runtime pack
• added wasm-bundled-timezones.a to workloads
• fixed TARGET_BROWSER detection for native/libs
• do not set TZ env variable to UTC as that's not valid timezone anyway. dotnet will fallback to UTC.
• create usr/share on browser VFS because it's mapped to SpecialFolder.CommonApplicationData which would not exist otherwise.
• rewrote EmitWasmBundleObjectFile as new EmitWasmBundleFiles
  • it can bundle any file not just assemblies
  • it can generate code to to wasi clang input stream or to files for emcc
  • it skips files which are already converted to
• new Target GenerateTimezonesArchive in both wasi.proj and wasm.proj
  • find all files to bundle, get hash for them
  • pass the list to EmitWasmBundleFiles Task
    • [for wasi] object files will be produced
    • [for emcc] compile source files to obj file after this
  • remove old source and object files
• updated Target _GenerateAssemblyObjectFiles to use new EmitWasmBundleFiles task

future work

• this will need SDK change for blazor
• next PR make BlazorEnableTimeZoneSupport work again,
  • when workload is available.
  • via something like Add feature-switch for invariant TimeZone support #37973
• make file bundling more incremental
• similar bundling could be used for WASI and ICU data files

[ghost]

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

Issue Details

---

work in progress

Author:	pavelsavara
Assignees:	pavelsavara
Labels:	arch-wasm, os-wasi
Milestone:	8.0.0

[pavelsavara]

I will need to deal with BlazorEnableTimeZoneSupport
See SDK and #37973

[pavelsavara]

@radical do you have further feedback ?

.

[radical]

LGTM 👍

[radical]

For a follow up PR, consider using EmccCompile task which compiles in parallel.

[pavelsavara]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ilonatommy]

Looks good, I especially like the description ✨

[pavelsavara]

CI failures are unrelated.

[pavelsavara]

Original size of dotnet.timezones.blat was 336270 bytes.
The size of new data embedded in the dotnet.wasm is 221991 bytes.

Some of the startup speed improvement is also caused by it.