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

Rename paragraph.py to format.py and add region formatting methods
from editor.py.  Add tests for the latter.
diff --git a/Lib/idlelib/configdialog.py b/Lib/idlelib/configdialog.py
index 807ff60..6ddbc7f 100644
--- a/Lib/idlelib/configdialog.py
+++ b/Lib/idlelib/configdialog.py
@@ -29,7 +29,7 @@
 from idlelib.autocomplete import AutoComplete
 from idlelib.codecontext import CodeContext
 from idlelib.parenmatch import ParenMatch
-from idlelib.paragraph import FormatParagraph
+from idlelib.format import FormatParagraph
 from idlelib.squeezer import Squeezer
 
 changes = ConfigChanges()