partially fix #355, a crude watcher

[HerringtonDarkholme]

No description provided.

[octref]

I don't think this should go in...I'm working on using something along this line and centralizing the file watching & version invalidation.

[HerringtonDarkholme]

I don't think we should rely on client behavior. As far as I know, few clients other than vscode itself support synchronization.

And I believe this is why tsserver also implents watching itself.

[octref]

Yeah then those clients need to implement it because Text Synchronization is part of LSP.

I'm not in a hurry to convert the file watching all to synchronization so other clients can continue to use VLS for now. However, if you want to have file watching not using synchronization, I suggest having just one watcher for all files (not in specific modes) and combine it with a better TextDocument manager that track versions and some meta info (think of a redux on the top of the server). This will help #681 and open door for #130.