[LNT] Code cleanup: consistently use space after comma

Summary:
Clean up uses of commas by having no space before the comma and a space
after. Likewise for the colon in dictionary values. This was produced by
running futurize's lib2to3.fixes.fix_ws_comma.

Reviewers: cmatthews, hubert.reinterpretcast, kristof.beyls, leandron, PrzemekWirkus

Reviewed By: cmatthews

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D69055

Author: Thomas Preud'homme