[Blazor] Modernize our Blazor JS assets and their delivery mechanism.

[javiercn]

• Generate ES6 modules by default. (P1)
  • This is a pre-condition so that we can reasonably breakdown our bundles into smaller items.
  • It enables other toolchains to post-process Blazor in order to perform further transformations.
  • It enables us to stop polluting the global window object as libraries can instead use import to get a hold to the Blazor instance.
  • We will still support opting in to register window.Blazor and window.DotNet on the document via a startup option.
  • This will be one more step towards support for running multiple Blazor instances on the same document.
• Break down Blazor web into multiple assets. (P1)
  • No concrete numbers for the enhanced SSR features of Blazor web, but it is likely less than 20KB
  • We should only pay for the wasm/server JS the moment we use it.
• Stop embedding JS files in Endpoints and Server assemblies, so they benefit from compression. Instead make them ship as static web assets. We can put them in the runtime pack for asp.net core and pick them in the SDK. (P1)
  • blazor.web.js goes from 180 KB to 43KB with brotli.
  • blazor.server.js goes from 146.58 KB to 35KB with brotli.

[javiercn]

Part of https://github.com/dotnet/aspnetcore/issues/52819

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s). If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.