Generic custom attributes don't work

[MichalStrehovsky]

See blocked test added in #78091.

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Issue Details

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See blocked test added in #78091.

Author:	MichalStrehovsky
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	-

[MichalStrehovsky]

I'm putting this into 7.0. We couldn't even compile generic attributes because S.R.Metadata had a bug that was crashing the compiler until very late in 7.0. We shipped generic attributes with pretty much no testing (#73735). It's pretty dissatisfactory.