Rename BuiltInTools dir to Dotnet.Watch

[tmat]

After moving dotnet-format to its own directory, the only remaining projects under BuiltInTools are dotnet-watch related.

[tmat]

@DustinCampbell @MichaelSimons ptal

[Copilot]

Pull request overview

This PR renames the src/BuiltInTools directory to src/Dotnet.Watch, consolidating all dotnet-watch related code under a single, more descriptive directory name. This is a large-scale refactoring that updates project references, solution filters, and documentation to reflect the new directory structure.

Changes:

• Renamed src/BuiltInTools directory to src/Dotnet.Watch
• Updated all project references from BuiltInTools to Dotnet.Watch across test and source projects
• Updated solution filters, CODEOWNERS, and documentation to reference the new path

Reviewed changes

Copilot reviewed 16 out of 223 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/dotnet-watch.Tests/dotnet-watch.Tests.csproj	Updated ProjectReference paths from BuiltInTools to Dotnet.Watch
test/Microsoft.WebTools.AspireService.Tests/Microsoft.WebTools.AspireService.Tests.csproj	Updated Import path to Dotnet.Watch
test/Microsoft.Extensions.DotNetDeltaApplier.Tests/Microsoft.Extensions.DotNetDeltaApplier.Tests.csproj	Updated ProjectReference and Import paths
test/Microsoft.DotNet.HotReload.Watch.Aspire.Tests/Microsoft.DotNet.HotReload.Watch.Aspire.Tests.csproj	Updated ProjectReference and Import paths
test/Microsoft.DotNet.HotReload.Test.Utilities/Microsoft.DotNet.HotReload.Test.Utilities.csproj	Updated ProjectReference path
test/Microsoft.DotNet.HotReload.Client.Tests/Microsoft.DotNet.HotReload.Client.Tests.csproj	Updated three Import paths
test/Microsoft.AspNetCore.Watch.BrowserRefresh.Tests/Microsoft.AspNetCore.Watch.BrowserRefresh.Tests.csproj	Updated ProjectReference path
src/WasmSdk/Tasks/Microsoft.NET.Sdk.WebAssembly.Tasks.csproj	Updated ProjectReference path
src/Layout/redist/redist.csproj	Updated ProjectReference path
src/Dotnet.Watch/* (many files)	All new files under the renamed directory containing moved source code
src/Dotnet.Watch/dotnet-watch.slnf	Updated solution filter with new paths
source-build.slnf	Updated project paths for source build
cli.slnf	Updated project path
CODEOWNERS	Updated ownership paths
eng/dotnet-format/validate.rsp	Updated validation path
documentation/specs/dotnet-watch-for-maui.md	Updated documentation reference

[tmat]

/ba-g Known Linux failure.