C++: Move Expr location workaround to Expr.qll

[jbj]

This workaround from DataFlowUtil.qll (#1781) should be useful for any query that selects an Expr. In particular, it's useful for IR data flow.

Internal PR: https://git.semmle.com/Semmle/code/pull/37020

To do:

• Run CPP-Differences and use the Profile Viewer.
• Accept test result changes in internal and external repo.

[jbj]

All the test changes in Language-Tests/CPP LGTM, and I think they just need to be accepted.

Because this PR conflicts with Absolutely Everything and will need a synced submodule update, I'm going to wait until a less busy time before proposing it for merge.

[jbj]

I'd like to get #3389 merged first, and then I can remove the getActualLocation predicate that's introduced (via rename) there.

[geoffw0]

QL changes LGTM.

Because this PR conflicts with Absolutely Everything

I assume the conflicts will be limited to tests, and perhaps mostly IR/dataflow tests, so not quite as bad as you describe here?

[jbj]

I assume the conflicts will be limited to tests, and perhaps mostly IR/dataflow tests, so not quite as bad as you describe here?

I think this will include tests in the internal repo, so there will also be potential conflicts on the submodule pointer.

[jbj]

Started https://jenkins.internal.semmle.com/job/Changes/job/CPP-Differences/1157/

[jbj]

I thought I'd picked a quiet time to get these conflict-prone changes merged, but apparently it was just the opposite. I can't complain about that.

The CPP-Differences results from yesterday should still be valid. Performance is unchanged, and there are two new results on a hidden-by-default query. Those results must have been there the whole time, just hidden because locations were missing.