Forbid incompatible foreach parameter types for AAs

[ntrel]

Fixes #21456.

This errors unless both:

• the AA component types implicitly convert to the respective foreach parameter types
• each of those type checks have types the same size

Although it would be better to support larger foreach parameter types, this prevents corruption for now.

Also improve error messages (see commits).

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#21463"

[rainers]

I don't think the comparison of the size is correct, the generated lambda should accept the correct parameter types instead. I have patched it here in foreachBodyToFunction: d2b3b00#diff-11fb0212c55c05ed6e743e6776abb3c56996381760c8725255c622f96f5d9d4bR4032, but that is part of the template implementation of AAs. Sorry, linking into the diff doesn't seem to work well.

[ntrel]

OK, so it looks like #21456 is fixed? I can split the error message part out of this PR.

[rainers]

It's not merged yet, but I can extract the fix to another PR. This will also cut down on #21066 a tiny bit.

[rainers]

see #21469