Fixes #6013, implement workspace/didChangeWatchedFiles

[tm1000]

This implements workspace/didChangeWatchedFiles

We also check to make sure the watch file that was changed is not currently open so this technically depends on #6010 being merged otherwise the files aren't tracked and there will be conflicts

[tm1000]

@weirdan it would still be nice to be able to get this merged in even though it will at some point in the future require a register call to function. Without the register call it won't break functionality.

The reason is that one of the older static analysis tools for php vscode was removed by Microsoft from the marketplace because it was no longer updated and caused stability issues. The maintainer of that is the same maintainer of the RPC and language server dependencies that Psalm itself uses.

Namely: https://github.com/felixfbecker/php-language-server and https://github.com/felixfbecker/php-language-server-protocol (@muglug seems to at least have access to the second one)

This pr actually brings Psalm almost to feature parity with the extension that was disabled from the marketplace. I'm linking that extensions issue list so you can see what I'm talking about: https://github.com/felixfbecker/vscode-php-intellisense/issues

[weirdan]

Thanks!