treat generic body type as atomic in iterOverType

[metagn]

follows up #24095

In #24095 a check was added that used iterOverType to check if a type contained unresolved types, with the aim of always treating tyGenericBody as resolved. But the body of the tyGenericBody is also iterated over in iterOverType, so if the body of the type actually used generic parameters (which isn't the case in the test added in #24095, but is now), the check would still count the type as unresolved.

This is handled by not iterating over the children of tyGenericBody, the only users of iterOverType are containsGenericType and containsUnresolvedType, the first one always returns true for tyGenericBody and the second one aims to always return false. Unfortunately this means iterOverType isn't as generic of an API anymore but maybe it shouldn't be used anymore for these procs.

[github-actions]

Thanks for your hard work on this PR!
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