[clang] [clang] Rename diag notes that assumed precompiled dependencies are pch's, NFCI (PR #142161)

[Volodymyr Sapsai via cfe-commits]

vsapsai wrote:

How natural is it to assume that "precompiled file" is the same-ish as "compiled file" aka "object file"? I'm wary of making users pay attention to such details. "Precompiled header" is an existing term, so I'm fine using it. But it is worth considering what are the differences and similarities in
* precompiled header
* compiled header
* precompiled file
* compiled file

https://github.com/llvm/llvm-project/pull/142161