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

[David Tarditi via cfe-commits]

dtarditi wrote:

@haoNoQ I believe the static analyzer can produce undefined values from out-of-bounds memory accesses also.   There are some test cases in this change that show that.

Some possible error message that I think  cover both cases are:
- `use of uninitialized memory or out-of-bounds memory`
- 'use of uninitialized or out-of-bounds memory`


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