Missing availability diagnostic on literal implicit init base type

[LucianoPAlmeida]

Describe the bug
No diagnostic is being emitted when base type for implicit init from literal expression is unavailable.

@available(*, unavailable)
struct S: ExpressibleByIntegerLiteral {
  init(integerLiteral value: Int) {}
}
@available(*, unavailable)
typealias IntegerLiteralType = S

let i = 0 // implicit resolves to S(integerLiteral: 0) but S is unavailable so we should emit availability diagnostic

Steps To Reproduce
Steps to reproduce the behavior:

1. Try compile the snippet above
   ...

Expected behavior
Unavailable diagnostic should be emitted.

Environment (please fill out the following information)

• Xcode Version/Tag/Branch: main at 66f6769