Currently `{inout, array, string}-to-pointer` conversion doesn't
track whether there was a difference in optionality between involved
types which leads to ambiguity when different overload choices
have different optionality requirements.
Let's fix that by increasing a score in cases if pointer type
is itself optional e.g.:
```swift
func foo(_ x: UnsafeMutablePointer<Int>) {}
func foo(_ x: UnsafeMutablePointer<Int>?) {}
foo(&foo) // Should pick the least optional overload choice.
```
Resolves: [SR-8411](https://bugs.swift.org/browse/SR-8411)
These include the pointer-to-pointer and pointer-to-buffer-pointer
initialiser parameters amongst a couple of others, such as
`Unmanaged.fromOpaque`, and the source for the `move[...]` family of
methods.
