Previously, the AbstractionPattern that was used for the value
"returned" (i.e. via a completion handler) from ObjC mostly (but not
quite always) was "type".
The generated completion handler correctly (because this is required in
order to call _resumeUnsafeContinuation) reabstracted the block (e.g.
from @convention(block) to @substituted <T> () -> @out T for <()>). The
callee of the ObjC function, however, loaded the function from the block
as if it were not reabstracted (e.g. () -> ()).
On most platforms, that happened to work. On arm64e, that difference in
types caused in a difference in pointer signing, resulting in a failure
at runtime.
rdar://85526879
rdar://85526916
Stopped validation-test/compiler_crashers_2_fixed/rdar79383990.swift
from trying to call -[NSBackgroundActivityScheduler scheduleWithBlock:]
async--that method is now annotated NS_SWIFT_DISABLE_ASYNC.
Previously, AbstractionPattern::getOpaque() was used for async
continuations. That was problematic for functions like
```objc
- (void)performVoid2VoidWithCompletion:(void (^ _Nonnull)(void (^ _Nonnull)(void)))completion;
```
whose completion takes a closure. Doing so resulted in attempting to
build a block to func thunk where one of the functions had an out
parameter.
Instead, use the AbstractionPattern(ty).
rdar://79383990
