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

[David Tarditi via cfe-commits]

dtarditi wrote:

Thanks - I updated the PR title and description so that it can be used for the commit.

It could be a little confusing to read the PR thread with the updated description.  Here is the original description, in case anyone reading the thread needs the context.

> A clang user pointed out that messages for the static analyzer undefined assignment checker use the term 'garbage'. This is kind of snarky and also imprecise. This change replaces the term 'garbage' in those messages with 'not meaningful'. It moves the term 'undefined' to be first in the messages because of the possible ambiguous parsing of the term 'not
meaningful and undefined'. That could be parsed as '(not meaningful) and undefined' or 'not (meaningful and undefined').
> The use of the term 'meaningless' was considered, but not chosen because it has two meanings in English. One meaning is 'without meaning'. The other meaning is 'having no point'. The 2nd meaning could be construed
as indicating the computation could be deleted.
> rdar://133418644






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