Isolate watchers from each other

[bpasero]

Our current file watching strategy is that many locations can ask to watch a path but the events will always be submitted through a single file service event without knowing the origin.

This means every extension that manages to create a file system watcher will still receive all events from all other watchers from other extensions.

Ideally we can isolate the request to watch in a way that the events returned are only for the request specifically. This will mainly avoid duplicate events, less likely wrong events which I think still cannot occur given our glob pattern matching.

[bpasero]

This is quite hard to achieve with our current API where a file system provider has a watch method:

vscode/src/vscode-dts/vscode.d.ts

Line 8252 in ca2ae28

watch(uri: Uri, options: { readonly recursive: boolean; readonly excludes: readonly string[] }): Disposable;

But all events go through the onDidChangeFile event without correlation back to the original watch request:

vscode/src/vscode-dts/vscode.d.ts

Line 8229 in ca2ae28

readonly onDidChangeFile: Event<FileChangeEvent[]>;

But we still can do something for avoiding duplicate events as reported in #163352: #169609