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

[Donát Nagy via cfe-commits]

NagyDonat wrote:

> Do you want me to condense the change to a single commit as recommended [here](https://llvm.org/docs/GitHub.html#landing-your-change)? Alternately, I could post a draft commit message in a comment for use with GitHub's UI for a squash-merge.

Please put a draft commit message in a comment, that would be easier for us in a GitHub squash-and-merge. Also note that you can directly edit the PR title and the description (first comment), which are combined by the GitHub UI to form the default commit message for the squash-and-merge  (which can be then manually edited).

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