fix subtype match of generic object types

[metagn]

split from #24425

Matching tyGenericBody performs a match on the last child of the generic body, in this case the uninstantied tyObject type. If the object contains no generic fields, this ends up being the same type as all instantiated ones, but if it does, a new type is created. This fails the sameObjectTypes check that subtype matching for object types uses. To fix this, also consider that the pattern type could be the generic uninstantiated object type of the matched type in subtype matching.

[github-actions]

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