[clang] [OpenACC][CIR] Implement member exprs for 'copy' lowering (PR #142998)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Nice job with the testing! I had a moment of panic seeing the size of this change, only to find that it's mostly test cases. I have a couple of questions, but it looks good.

Honestly you're not wrong :)  I wrote all of these tests in advance expecting this to be 6-7 different patches.  Then while implementing the first bit, I found myself realizing that I'd already inadvertently already implemented the others so just completed the tests.

Much of the testing is a little redundant, and likely is overkill, but it seems sensible to keep them around even so.

>Is a case like this possible?
I've now pushed THIS case ot the test file.  it has `cir.ptr_stride` uses in it, but not in a way that is problematic, and I think it just works correctly.    Thanks for the test case!

https://github.com/llvm/llvm-project/pull/142998