Issue #16473: Fix byte transform codec documentation; test quotetabs=True

This changes the equivalent functions listed for the Base-64, hex and Quoted-
Printable codecs to reflect the functions actually used. Also mention and
test the "quotetabs" setting for Quoted-Printable encoding.
diff --git a/Lib/encodings/quopri_codec.py b/Lib/encodings/quopri_codec.py
index 0533dbe..496cb76 100644
--- a/Lib/encodings/quopri_codec.py
+++ b/Lib/encodings/quopri_codec.py
@@ -11,7 +11,7 @@
     assert errors == 'strict'
     f = BytesIO(input)
     g = BytesIO()
-    quopri.encode(f, g, 1)
+    quopri.encode(f, g, quotetabs=True)
     return (g.getvalue(), len(input))
 
 def quopri_decode(input, errors='strict'):