Issue Description:

import Foundation
func testTypeInferClosureArg(data: Data, array: inout [UInt8]) {
  data.withUnsafeBytes { (rawBuffer: UnsafeRawBufferPointer) in
    // I intentionally forgot the "contentsOf:" label here...
    array.append(rawBuffer)
  }
}

I intentionally forgot the "contentsOf:" label when passing the closure argument, rawBuffer, into array append. This version of array append takes a single Element, UInt8, rather than a sequence of those elements.

I expect to get an error at the call to array.append, stating that UnsafeRawBufferPointer cannot be converted to UInt8.

Instead I get this error:

 error: 'UnsafeRawBufferPointer' is not convertible to 'UnsafePointer<_>'
  data.withUnsafeBytes { (rawBuffer: UnsafeRawBufferPointer) in
                         ^

The type checker appears to be picking the wrong overload of withUnsafeBytes ❓ even though the argument type is explicitly provided. This is a problem because the diagnostic instructs the programmer to use the old deprecated API, potentially exposing undefined behavior.

Note that when I remove the closure argument type, I get this error:
"type of expression is ambiguous without more context"

Which prompts me to add the closure argument type. Never do I get an error pointing to the incorrect array.append call.

This problem isn't specific to array.append--that's just an easy way to demonstrate it. It seems to occur whenever the expression type checker fails to resolve something inside the closure...