[blazor] startup sequence unification

[pavelsavara]

Summary

This unifies the startup sequence with the runtime.

Contributes to dotnet/runtime#74346
Depends on dotnet/runtime#81886

Changes

• we create runtime instance using the new create API
• DLLs and PDBs are loaded by runtime
• timezone data is loaded by runtime
• ICU data is filtered by Blazor and loaded by runtime
• environment variables are set by the new API
• Blazor._internal is initialized after runtime instance creation
• reorganized order of methods in the file for better readability
• disabled runtime's feature throttling of parallel downloads

Fixes

• fixed setting LANG environment based on applicationCulture option even if ICU is not sharded to make it work according to docs
• improved ICU test LoadingApp_KoreanLanguage_Works

Should still work as before

• download progress bar
• resourceLoader (cache)
• lazy and satellite assemblies

Out of scope

• choosing ICU shard after [wasm][icu] ICU files sharding + custom icu data loading for WASM runtime#80421
• The list of assets is transformed form existing blazor.boot.json into existing mono-config.json schema. Unification of schema will be separate work.
• runtime could do throttling of parallel downloads, I disabled the feature for Blazor in this PR, until we decide that it's useful here too.

[ilonatommy]

Looks good from my perspective.

[MackinnonBuck]

Looks good to me 🙂

[maraf]

LGTM 👍