Add array.clear()

Bug report

from array import array

x = array("B")
x.clear()    # AttributeError: 'array.array' object has no attribute 'clear'

But array is a MutableSequence, so we expect the clear() method to be implemented.
If this is correct, then I'm ready to work on PR.

Original issue from the typeshed repository: python/typeshed#11008

CPython main branch

Linux

pythongh-114894: add array.array.clear() method

gh-114894: add array.array.clear() method (#114919)

Thanks for your contribution!

pythongh-114894: add array.array.clear() method (python#114919)