[mono] Allow RuntimeType arguments in CustomAttributeBuilder

[uweigand]

• Fixes[mono] CustomAttrBuilder does not support RuntimeType arguments #58019

[jkotas]

Do we need to add test?

[SamMonoRT]

@uweigand - can we get a test added for the change ?

[uweigand]

@uweigand - can we get a test added for the change ?

Turns out there was already a test case, but disabled on Mono. Re-enabling the test case showed the failure fixed by this PR originally, and it also fails because of another reason: the Mono implementation rejected a null field value of Array type, which CoreCLR accepts and the test case uses. I've added a fix for this second issue as well, and re-enabled the test case.

[ghost]

Hello @marek-safar!

Because this pull request has the auto-merge label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

p.s. you can customize the way I help with merging this pull request, such as holding this pull request until a specific person approves. Simply @mention me (@msftbot) and give me an instruction to get started! Learn more here.

[srxqds]

@marek-safar could this backport to release/6.0?

[lambdageek]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1177581011