[CIR][NFC] Add errors for unhandled AggExprEmitter visitors (#155469)

There are a lot of required handlers in AggExprEmitter that are
currently missing. Because the ASTVisitor has fallbacks, this means we
just silently ignore whatever expressions are not explicitly handled.
This patch adds handlers where we know they will be needed and just
issues a diagnostic.

This exposed failures in a few tests. In one case, we should have
handled constant initialization earlier, which would have avoided going
to the AggExprEmitter at all. I added a stub with a missing feature
marker to allow that case to work as it had. Another test required us to
ignore cast expressions that should be ignored, so I partially
implemented the cast visitor. Finally, there's a case where the test was
just accepting a bad result. I changed that case to XFAIL until it can
be properly fixed.

0 files changed, 0 insertions, 0 deletions