Language service wants all files to end in *.ts or *.d.ts

[jrieken]

I have noticed that bad things happen when the language service host provides a list of file names that don't end in *.ts nor *.d.ts. I strongly opt for relaxing this because often buffers are not saved yet (no filename, just some tmp-path) and will not be saved (like the playground editor)

[mhegazy]

should be handled by PR #987

[mhegazy]

@jrieken can you give it a try and let us know how it fares.