`javascript.validation.enabled` editor setting controls typescript validation as well

[weswigham]

For future travelers just in case it's useful, I had "javascript.validate.enable": false because I didn't want JS files specifically to be checked. Looks like with the native preview that setting is now interpreted as a blanket disabling of typescript checking across the board.

Originally posted by @elramus in #4587

According to @DanielRosenwasser, this isn't actually intentional and just kinda fell-out from the unified config handling we setup to handle falling back from the js/ts -> typescript -> javascript config namespaces.

[jakebailey]

Yeah, so the fix here is going to be to start doing language-scoped settings, but I think we could probably special case just this one thing?

[weswigham]

IMO, this and format.enabled are the big "wait, why do these toggle unexpected file extensions, too".