Add sourcemap.sourcemapFile configuration

[TRHeliad]

Adds an extension configuration for choosing the name of the sourcemap.

There is actually an issue I noticed with unregistering watched files. I am not experienced in working with an LSP so I'm not really sure why the message I am sending to unregister didChangedWatchedFilesCapability isn't actually stopping vscode from sending file changed messages for the sourcemap.

[TRHeliad]

@JohnnyMorganz do you know anything about unregistering capabilities and why it might not be working? This isn't really a huge issue because if you reload the workspace after changing config it won't be watching.

[JohnnyMorganz]

I'm not too familiar. If you set your logging level to verbose, do you get a response to your unregister capability request?

[TRHeliad]

Looks like the LSP spec has a little typo so my parameter name was wrong. The unregistration gets a success response now, however vscode still seems to be watching the sourcemap if sourcemaps were enabled by the configuration earlier in the same session. Seems like it is out of my hands, but shouldn't be a big deal since you can reload to window if you don't want it watched.

[TRHeliad]

Closes #661

[JohnnyMorganz]

Thanks, and so sorry for the delay!

Overall looks good to me, I did a slight change to make the ID different that we register for sourcemap watching compared to standard watching. Since we don't want to deregister the default watcher when we actually just want to deregister sourcemap watching.

Do you mind giving a quick check to see if this still works? Otherwise I can merge it in

[TRHeliad]

Just pushed a fix I forgot to add. Tested and working for me.

[JohnnyMorganz]

Thanks!