[clang-format] Adds space around angle brackets in text protos

Summary:
This patch adds spaces around angle brackets in text proto Google style.
Previously these were detected as template openers and closers, which happened
to have the expected effect. Now we detect them as scope openers and closers
similarly to the way braces are handled in this context.

Reviewers: djasper

Reviewed By: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D42727

llvm-svn: 324337