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

[Donát Nagy via cfe-commits]

NagyDonat wrote:

> So I'm still mildly in favor of simply saying "uninitialized". It may or may not be someone else's actively used memory but that's beyond the programmer's control and they know it (hopefully). It would be somewhat dishonest to give the user an impression that this checker has considered the object's bounds before emitting a warning. Both the checker and the engine itself effectively ignore allocation bounds for all intents and purposes.

I'm seconding this.

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