[Sema][NFC] Move two misplaced uninit tests to clang/test/SemaCXX (#128013)

Because they are the last two remaining test files that appeared under
`clang/test/Analysis` but were unrelated to the clang static analyzer.
For background see the following discourse thread:
https://discourse.llvm.org/t/taking-ownership-of-clang-test-analysis/84689/2

I placed them in in `clang/test/SemaCXX` because they are testing the
`-Wuninitialized` warning family and the other tests of this feature can
be found there (or in `Sema`, `SemaObjC` depending on the language).

Note that `clang/test/Analysis` contains many other test files named
`uninit-*`, but those test the uninitialized value handling of the clang
static analyzer, which is independent of the (non-path-sensitive)
compiler warnings that are tested in the two files that I'm moving.

Also note that the implementation of the `-Wuninitialized`-like warnings
relies on the source files `clang/lib/Analysis/UninitializedValues.cpp`
and `clang/lib/Sema/AnalysisBasedWarnings.cpp`, and this would
theoretically justify leaving their tests in the "Analysis" directory;
but in practice the "Analysis" directory is almost exclusively used by
the static analyzer, so I still decided to relocate these two tests for
the sake of consistency.

Author: NagyDonat