add explicit flag to replace_reason_const calls (part 6)
add explicit flag to replace_reason_const calls (part 6)

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: D17054222

fbshipit-source-id: a4491062ca01bd7c09428af308ebd21b5d5f675c

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