Chef Refactor (#18009)

* Chef - Add stateful_shell.py and constants.py

Change-Id: Ia59a3d2a71204e4af2c41d6192d47f048a58c3b4

* Chef - Print splash text

Change-Id: I9b162cabab700e87f12806668b2953bf57348449

* Chef - Use textwrap.dedent on textblocks

Change-Id: I861f24ac20d440cf4a3e605809421a766ecdd476

* Chef - Remove use of commandQueue

Change-Id: I75d5ae6fea25c6b933cb9823a29e9c2224b8188d

* Chef - Replace shell writes with Python open() calls

Change-Id: I0147fa6b96d3a15bf95352acbd136e8f1e648b8f

* Chef - Make paths into global constants

Change-Id: Ib177d584bcd463aaafe10f4f338a90d6b234c3f1

* Chef - Remove HexInputToInt

Change-Id: Iebe5e76c169951e842262530d3feba5ac899a33c

* Chef - Remove unused statements

Change-Id: I56670e31722348fb47a1e59d2651cdcf3f983e28

* Chef - Convert variables to snake case per PEP8

Change-Id: I52520eec1dfb8093c39ce4570aa99cdd0b0d854a

* Chef - Add function type hinting

Change-Id: Ib82f0bf4752819b65d2c76058429931c6986bd83