Prepare Browser Refresh Server for sharing

[tmat]

Defines AbstractBrowserRefreshServer as a base implementation of Browser Refresh Server that can be shared between dotnet-watch, VS and VS Code.

Introduces WebApplicationAppModel as a base class for app models of web projects: WASM, WASM Hosted, and regular web server app (WebServerAppModel).
Moves most web project specific logic to WebApplicationAppModel.

Moves launch environment configuration to shared code.

Fixes #47685

[github-actions]

This PR is targeting main, which is now for .NET 11-facing work. If you intended to target .NET 10, either retarget this PR to release/10.0.1xx or make sure you backport the change to release/10.0.1xx after merging. See #50394 for more details.

[dotnet-policy-service]

Thanks for your PR, @@tmat.
To learn about the PR process and branching schedule of this repo, please take a look at the SDK PR Guide.

[tmat]

@DustinCampbell ptal