[3.14] gh-141692: Add a slice-specific lib folder to iOS XCframeworks. (GH-141693) (#141733)

Modifies the iOS XCframework to include a lib folder for each slice that
contains a symlinked version of the libPython dynamic library.
(cherry picked from commit 7b0b70867586ef7109de60ccce94d13164dbb776)

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>