[3.15] gh-153419: Fix several issues around bytearray __init__ (GH-153498) (#154622)

[3.15] gh-153419: Fix several issues around bytearray __init__ (GH-153498) (#154622)

gh-153419: Fix several issues around bytearray __init__ (GH-153498)

Introduce a bytearray_new() function to ensure that
ob_bytes_object is always set on a bytearray.

Resizing a bytearray to 0 length now explicitly sets
the ob_bytes_object to the empty constant immortal.

Add a check in the 'bytearray init from string'
fast path to ensure there are no active exports.

This fixes asserts/crashes on the following:
 - bytearray(1).__init__()
 - bytearray().__new__(bytearray).append(1)
 - a = bytearray(); b = memoryview(a); a.__init__('x', 'ascii')
(cherry picked from commit d5c1b29658063d1ef9d66515d8e4cb9929126be7)

Co-authored-by: Steve Stagg <stestagg@gmail.com>
Co-authored-by: Cody Maloney <cmaloney@users.noreply.github.com>