[CI] Refactor compute_projects to Introduce Meta Projects
This patch introduces the concept of meta projects into the
compute_projects script. Meta projects are projects like CIR and
GoogleTest where they do not have their own top level project. This
patch adds a little bit of extra code in exchange for making meta
projects a first level concept that can be configured almost entirely by
changing around the mappings at the top of the file. This patch also
refactors the project skipping functionality to use meta projects.
This (arguably) makes the CIR support a little bit cleaner and is
necessary for some future improvements like running all the tests on
Github workflow changes and running tests when third-party changes.
Reviewers: Endilll, andykaylor, lnihlen, gburgessiv, dschuff, Keenuts, cmtice
Reviewed By: andykaylor
Pull Request: https://github.com/llvm/llvm-project/pull/150249
