[blazor] Use JSImport for lazy loading assemblies

[pavelsavara]

Motivation

• The current getLazyAssemblies is implemented using legacy/obsolete JS interop.
• legacy interop has problems with multi-threading and uses unsupported API.
• legacy interop is not CSP compliant

Contributes to #37787

Description

• use new generated JavaScript interop with [JSImport]
• moved async parallel download to C# side
• only one allocation & copy of the DLL bytes from fetch buffer directly to wasm memory.
• the new implementation is loading DLLs asynchronously as they arrive, which should be faster overall

[pavelsavara]

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[maraf]

LGTM 👍

[ilonatommy]

I like it, the new version is easier to read. The only idea I got was: can we have names in resources in plural form? resources.lazyAssembly, resources.pdb, resources.assembly -> resources.lazyAssemblies, resources.pdbs, resources.assemblies

[pavelsavara]

I like it, the new version is easier to read. The only idea I got was: can we have names in resources in plural form? resources.lazyAssembly, resources.pdb, resources.assembly -> resources.lazyAssemblies, resources.pdbs, resources.assemblies

Those are from blazor.boot.json and I think we may need to keep it backward compatible.

[MackinnonBuck]

LGTM! Just added some nits, feel free to ignore if you disagree with the changes.