Add clang tidy script and use it during pre-submit builds

Adds a new file on the same basis as clang-format.sh and copyright.sh that allows running clang-tidy as a script instead of building the source with it. This script can be run on changed files or on the whole source tree, but will often involve checking all files that have been affected by a change.

In CI, the default is to longer compile the source in the clang-tidy job, but just to run the script instead.

The clang-tidy:build job is now only run during schedules instead of for all builds.