swift234

Rename UnsafePointer allocate & deallocate. (#3608)

As proposed in SE-0107: UnsafeRawPointer:
Rename 'init(allocatingCapacity:)' to 'UnsafeMutablePointer.allocate(capacity:)'
Rename 'deallocateCapacity' to 'deallocate(capacity:)'

`allocate` should not be an initializer. It's primary function is to allocate
memory, not initialize a pointer.