This converts the ci/format.sh script to a Dart script that uses process_runner and isolates to multi-process the clang-format, diffs, and grepping needed to do the formatting changes.

It also will (by default) only check the formatting of changed files.

The user can optionally check all files (--all-files) or do only some types of checks with --check. --verbose prints the versions of the tools used for Clang format and Java format.

Specifying --fix will cause any formatting errors that would have been detected to be fixed.