[clang] [analyzer] Update the undefined assignment checker diagnostics to not use the term 'garbage' (PR #126596)

[Balazs Benics via cfe-commits]

steakhal wrote:

Hi, just to be sure I understand you correctly, by snarky, you mean "garbage" has a negative co-notation?
I'm not a native speaker, so please help me understand your and your user's perspective.

I'm in general open for changing the diagnostic message, but we should also consider the friction such renames can cause. Usually tools like CodeChecker or other frontends hash the messages, thus if it changes, the suppressions may not work ask expected before and after the rename.

/cc @NagyDonat for a CodeChecker opinion

https://github.com/llvm/llvm-project/pull/126596