Introduce -print-before-changed, making -print-changed also print before passes that...

Introduce -print-before-changed, making -print-changed also print before passes that modify IR

Summary:
Add an option -print-before-changed that modifies the print-changed
behaviour so that it prints the IR before a pass that changed it in
addition to printing the IR after the pass. Note that the option
does nothing in isolation. The filtering options work as expected.
Lit tests are included.

Author: Jamie Schmeiser <schmeise@ca.ibm.com>

Reviewed By: aeubanks (Arthur Eubanks)

Differential Revision: https://reviews.llvm.org/D88757