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

[Donát Nagy via cfe-commits]

NagyDonat wrote:

> > I completely agree that the message sounds a bit too much like "your code is garbage" and that's not very nice.
> 
> Ohh, now I see how this could be interpreted in a negative way. I never thought of this.
> 
> I like where the discussion is heading with emphasizing the use of "uninitialized". I also wonder if the sibling checkers of this one also use this "garbage" wording for their diagnostics. If so, we should also consider changing those if we are at it.

The message clearly says that the **value** is garbage :roll_eyes:

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