[SIL.rst] Add to copy_value's docs that in non-Raw SIL, one cannot give copy_value a move only value as an operand.
[SIL.rst] Add to copy_value's docs that in non-Raw SIL, one cannot give copy_value a move only value as an operand.

I am enforcing this in the verifier, so it makes sense to document in SIL.rst.

roambotics/swift,benlangmuir/swift,apple/swift,roambotics/swift,benlangmuir/swift,apple/swift,glessard/swift,roambotics/swift,glessard/swift,benlangmuir/swift,glessard/swift,glessard/swift,roambotics/swift,apple/swift,apple/swift,glessard/swift,benlangmuir/swift,roambotics/swift,benlangmuir/swift,roambotics/swift,glessard/swift,benlangmuir/swift,apple/swift,apple/swift