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

[Artem Dergachev via cfe-commits]

haoNoQ wrote:

The most common "exotic" memory location is probably uninitialized heap memory: https://godbolt.org/z/h9MPzn7EP (We have tests for this right? ...right?) So in this case we need to make sure the user doesn't think that we're talking about the pointer variable (esp. when it's the only variable around).

We can also try to simply call it "memory", e.g. "increment over uninitialized memory", or something more verbose of that nature.

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