[Prototype] Typed browser platform APIs for Blazor, starting with Web Storage

[jsakamotoIGJP]

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A prototype of typed browser platform APIs for Blazor

Description

A draft for design feedback, not a request to merge. Milos asked me to open it here so that @maraf and @javiercn can review it. The API proposal is #69304.

This adds Microsoft.AspNetCore.Components.Platform, which gives typed access to standard browser APIs instead of string-based IJSRuntime calls. The first family is Web Storage. DOM APIs and application-specific JavaScript are out of scope.

• IBrowserPlatform, Window, Storage, and AddBrowserPlatform.
• LocalStorage and SessionStorage are extension properties on Window, so the trimmer can remove the one an application does not use.
• ProtectedLocalStorage and ProtectedSessionStorage use the projection for their default registration. Their public constructors still work.
• Unit tests, coverage for the new registrations in Microsoft.AspNetCore.Components.Server.Tests, and a test application with E2E tests for Interactive Server and WebAssembly.
• .github/skills/port-components-platform-api/SKILL.md, which writes down the rules for adding the next family, including the trimming one.

The first two commits are by @kotlarmilos, from kotlarmilos#1 and kotlarmilos#2, rebased on the current main. Javier already reviewed the prototype and asked to remove the lock in Storage, which a later commit does.

Questions

1. Shared framework, or a separate package? It is a separate package today, but Microsoft.AspNetCore.Components.Server is in the shared framework and references it.
2. The E2E tests do not run in CI, and that is on purpose. I left PlatformTestApp.E2E.Tests out because this is a prototype.
3. Extension properties cost discoverability. Without the namespace import, the editor does not suggest LocalStorage after you type Window.. Normal properties are easier to find, but then the trimmer cannot remove the unused one.
4. The skill file states the design rules this prototype follows. Please review it alongside the code, or tell me to drop it if it doesn't belong in this PR.

[dotnet-policy-service]

Hey @dotnet/aspnet-build, looks like this PR is something you want to take a look at.

[dotnet-policy-service]

Thanks for your PR, @jsakamotoIGJP. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsakamotoIGJP]

I know some CI checks failed. I'll fix them later.

[jsakamotoIGJP]

Aside: The build is still failing, but I'm sure that the only red item now is a flake that this change doesn't touch.

Here is what changed since I opened this, and what I need decisions on.

Fixed

• The lock in Storage, which Javier asked about in the prototype review.
• GetLengthAsync passed CancellationToken.None, and any token turns off the default JS interop timeout. It now uses the overload without a token.
• Storage and Window implemented IAsyncDisposable publicly. Window creates them and hands the same instance to every caller, so a dispose from application code broke the rest of the scope. Both implement the interface explicitly now, and disposal only releases the JS reference.

Reverted, and this is the decision I need first

I temporarily reverted the adoption in ProtectedLocalStorage and ProtectedSessionStorage. Microsoft.AspNetCore.Components.Server is in the shared framework and cannot reference a package that is not, so every build leg failed. Moving these features into the shared framework would fix it, but that settles the packaging question on its own. @kotlarmilos, which way do you want to go?

Still open

1. The E2E tests do not run in CI. Projects under testassets are excluded in eng/Build.props and added back one at a time, and I left PlatformTestApp.E2E.Tests out because this is a prototype. Tell me if you want it in the build.
2. .github/skills/port-components-platform-api/SKILL.md came from the prototype branch, and I added the rules we learned in review. Keep it here, or drop it from this PR.

The branch is rebased on the current main with a linear history, and the first two commits are still by @kotlarmilos.