clang-format vs plugin: bake clang-format.exe into the vsix

This makes the clang-format plugin self-contained. Instead of
requiring clang-format.exe to be available on the PATH, this
includes it in the plugin's installer (.vsix file) and runs it
from the install directory.

Differential Revision: http://llvm-reviews.chandlerc.com/D2281

llvm-svn: 196122