add explicit flag to replace_reason calls (part 4)
add explicit flag to replace_reason calls (part 4)

Summary: `def_loc` would be dropped by default when replacing descriptions. I want to make it such that either `def_loc` and `annot_loc` are preserved (indicating some sort of derived reason), or they are explicitly dropped (indicating a new reason). APIs will be renamed later.

Reviewed By: panagosg7

Differential Revision: D17054282

fbshipit-source-id: 9dfe9a171dd17c9ccc74003f3c3fbbed0f15d8f6

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow