Update test checks for Clang-Doc

UTC is a valuable utility for LLVM developers to update tests due to mechanical changes in codegen that affect a lot of tests.

Like those LLVM passes, changes to Clang-Doc's templates or core data structures often cause a lot of churn in our test output.

It would be best if we had a utility, like UTC that could update our test outputs in a maintainable way.

This could be done either by extending some of the functionality in the UTC scripts, or by writing our own version that reuses the UTC modules.

Start by examining the existing UTC scripts and reusable UTC modules, then review how Clang-Doc tests record expected output. Compare extending UTC with creating a Clang-Doc-specific utility; done means maintainable test-output updates cover template or core data-structure changes without manual churn.

Written by the indexing model from the issue text.