[clangd][vscode] clang-format the the extension code.

Summary:
As we are going to grow the extension in the near future, it is time to
formalize the TS code format/style of our extension (although we'd lose the
history).

We use default options of clang-format:
- 80 max line length
- 2 space indent

Reviewers: ilya-biryukov, sammccall, jvikstrom

Subscribers: MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65657

llvm-svn: 367684