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

[Artem Dergachev via cfe-commits]

haoNoQ wrote:

So when it comes to the ArrayBoundChecker, the checker that checks that every access is within bounds, I think that its underlying "model" should be enabled by default, so that to proactively terminate execution paths on which uninitialized accesses happen. It should probably even be considered part of `core` (i.e. we don't support turning it off under any circumstances).

And if this means losing some of those uninitialized read warnings by default, that's probably for the best. Because, well, they work and behave the same way as other ArrayBoundChecker warnings. It is likely that these "uninitialized" read warnings are desired _if and only if_ ArrayBoundChecker warnings are desired.

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