bpo-36390: IDLE: Combine region formatting methods. (GH-12481) (GH-14811)

Rename paragraph.py to format.py and add region formatting methods
from editor.py.  Add tests for the latter.
(cherry picked from commit 82494aa6d947c4a320c09c58fe0f100cdcf7af0b)

Co-authored-by: Cheryl Sabella <cheryl.sabella@gmail.com>
7 files changed