This patch works towards consolidating all Clang debug-info into the
`clang/test/DebugInfo` directory
(https://discourse.llvm.org/t/clang-test-location-of-clang-debug-info-tests/87958).

Here we move only the `clang/test/CodeGen` tests.

The list of files i came up with is:
1. searched for anything with `*debug-info*` in the filename
2. searched for occurrences of `debug-info-kind` in the tests

I created a couple of subdirectories in `clang/test/DebugInfo` where I
thought it made sense (mostly when the tests were target-specific).

There's a couple of tests in `clang/test/CodeGen` that still set
`-debug-info-kind`. They probably don't need to do that, but I'm not
changing that as part of this PR.