clang-format: [JS] space between pseudo keywords and template literals.

Summary:
Before:
  yield`foo`;

After:
  yield `foo`;

This reinstates commit 71d3b5cd91 / r307023 and fixes the logic by
introducing an explicit table of JavaScript pseudo keywords.

Reviewers: djasper

Subscribers: klimek

Differential Revision: https://reviews.llvm.org/D34953

llvm-svn: 307087