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

[Artem Dergachev via cfe-commits]

haoNoQ wrote:

Should we try to avoid calling the *value* uninitialized? Technically you initialize variables (or memory), not values. In the static analyzer terminology in particular, it's somewhat important that values are seen as immutable data that's temporarily associated with mutable memory. I think the rest of the static analyzer does an ok job making this distinction.

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