File watcher: ignore directories, allow watching non-recursively

[tmat]

Preparing directory watcher for watching individual files in some cases when we don't want to watch the entire directory tree (e.g. targets and props files outside of the project dir).

Fixes #49307

[dotnet-policy-service]

Thanks for your PR, @@tmat.
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[tmat]

@phil-allen-msft @DustinCampbell ptal

[Copilot]

Pull Request Overview

This PR extends the file-watching subsystem to distinguish between recursive and non-recursive watching and to ignore directory events, while centralizing path adjustments in PathUtilities and updating corresponding tests.

• Add an includeSubdirectories flag throughout the watcher factory, polling and event-based watchers.
• Filter out directory change events in both polling and file‐system–based implementations.
• Introduce PathUtilities.EnsureTrailingSlash and NormalizeDirectorySeparators.
• Update tests to drive the new behavior and adjust assertion ordering.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/dotnet-watch.Tests/FileWatcherTests.cs	Pass watchSubdirectories to tests and simplify assertion sorting
src/BuiltInTools/dotnet-watch/Utilities/PathUtilities.cs	Add trailing-slash and separator-normalization helpers
src/BuiltInTools/dotnet-watch/Internal/FileWatcher/PollingDirectoryWatcher.cs	Add _includeSubdirectories, rename and scope file dictionaries
src/BuiltInTools/dotnet-watch/Internal/FileWatcher/EventBasedDirectoryWatcher.cs	Honor IncludeSubdirectories and ignore directory events
src/BuiltInTools/dotnet-watch/Internal/FileWatcher/IDirectoryWatcher.cs	Switch to file-scoped namespace and add summary doc
src/BuiltInTools/dotnet-watch/Internal/FileWatcher/FileWatcherFactory.cs	Overload CreateWatcher to accept includeSubdirectories
src/BuiltInTools/dotnet-watch/Internal/FileWatcher/FileWatcher.cs	Split recursive vs. non-recursive watchers and update disposal
src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs	Propagate includeSubdirectories when watching containing dirs
src/BuiltInTools/dotnet-watch/DotNetWatcher.cs	Propagate includeSubdirectories for root project directory watch

Comments suppressed due to low confidence (2)

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/FileWatcher.cs:30

• Dispose only iterates _directoryTreeWatchers; non-recursive watchers in _directoryWatchers remain undisposed and can leak events—include both collections in disposal.

foreach (var (_, watcher) in _directoryTreeWatchers)

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/FileWatcher.cs:78

• When registering a recursive watcher, you remove redundant recursive watchers but leave non-recursive watchers intact; also clear entries in _directoryWatchers under the new root to avoid duplicate event streams.

var watchersToRemove = _directoryTreeWatchers