Add compilation/JS-beautify/html-beautify/etc to snippet validation checks (or lint rule)

[Zlatkovsky]

(Doesn't impact product code, only build script)

Essentially, make sure that when https://github.com/OfficeDev/office-js-snippets/blob/master/config/build.ts is run, it compiles (to catch compile errors & moved/renamed APIs, formats, etc.) the snippets.

https://github.com/OfficeDev/office-js-snippets