1. python script wrapper to call clang-format over the whole code base
2. Add clang-format rule `IncludeBlocks: Preserve` to tell clang-format
do not merge include blocks
3. Fix existed clang-format issue in code base

Bug: angleproject:3532
Change-Id: I289292dc62c2784ff21688065c87c3f3f5538f17
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1709720Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>