A call like ReplaceAddress(address, 0) is pretty ambiguous; so is
ReplaceAddress(address, false), so use an enum class that tells people
straight-up what the replacer is.
This also gets rid of the really weird naming, where if 'blr' is true,
we'd be replacing the address with a NOP, rather than an actual BLR
instruction, so we invert that so it actually makes sense. There's no
actual bug fixed here though, considering the OnInsert functions
specified the correct values; it's literally just weird naming.
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