Update UnmanagedCallersOnlyAttribute API surface#37843

Merged

AaronRobinsonMSFT merged 8 commits intodotnet:masterfrom AaronRobinsonMSFT:runtime_37612

Jun 23, 2020

+118-31

Commits on Jun 15, 2020

UnmanagedCallersOnlyAttribute should not be inheritable.
AaronRobinsonMSFT
committed

Commits on Jun 20, 2020

Ignore calling conventions that don't apply.
AaronRobinsonMSFT
committed
Remove allocation and length compute cost for string constant compare.
AaronRobinsonMSFT
committed
Fix logical error in generic BeginWith() function.
AaronRobinsonMSFT
committed