add explicit flag to replace_reason calls (part 3)
add explicit flag to replace_reason calls (part 3)

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: D17054278

fbshipit-source-id: 090bbb34d3ebc8d05ce9d12b5d5b33a46b487636

mroch/flow,samwgoldman/flow,gabelevi/flow,facebook/flow,gabelevi/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,samwgoldman/flow,gabelevi/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,gabelevi/flow,gabelevi/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,mroch/flow,samwgoldman/flow,gabelevi/flow,facebook/flow