duplicates:

• SR-11147 Add withUnsafeBufferPointer<T: HomogeneousAggregate, Result>

relates to:

• SR-3590 Implicitly convert &Tuple to UnsafePointer<Tuple.Element>
• SR-4649 Don't require & to pass value to UnsafeRawPointer
• SR-5048 Tuples of homogenous contents should adopt a common protocol

Issue Description:

We should implement implicit conversion from homogeneous tuple arguments to UnsafePointer as follows:

func get(_ p: UnsafePointer<Int>, at index: Int) -> Int {
return p[index]
}

let tuple = (0, 1, 2)
_ = get(tuple, at: 0)

Otherwise, users need to create a mutable copy of the tuple before converting it to a pointer. This is primarily for users working around the absence of fast fixed size arrays in the language.

I'm filing this for completeness, because we want language consistency across all these bugs:

• Support inout homogeneous tuple argument conversion to UnsafeMutablePointer<Element>.
  See [SR-3590] Implicitly convert &Tuple to UnsafePointer<Tuple.Element>.
  (source breaking in ridiculous cases)

• [SR-1956] `withUnsafePointer` shouldn't take its argument as `inout`
  (additive... we don't need to ban the inout syntax)

• Allow non-homgenous non-inout tuple arguments to be converted to UnsafeRawPointer.
  [SR-4649] "Don't require & to pass value to UnsafeRawPointer", is that it seeks to
  (additive)