[clang] [clang][ThreadSafety] Enable late parse for all capabilities, under the experimental flag (PR #212615)

[Marco Elver via cfe-commits]

melver wrote:

This is a substantial change, even though it looks benign on surface.

What is the concrete motivation? Is there real code where this is needed?

The problem with late-parsed attributes is that parsing is expensive, and so it had been applied selectively.

cc @rapidsna 

https://github.com/llvm/llvm-project/pull/212615