[RISCV] Untangle instruction properties from VSETVLIInfo [NFC]

The abstract state used in the data flow should not know anything about the instructions which produced the abstract states. Instead, when comparing two states, we can simply use information about the machine instr at that time.

In the old design, basically any use of the instruction flags on the current (as opposed to a "Require" - aka upcoming state) would be a bug. We don't seem to actually have any such bugs, but we can make this much more obvious with code structure.

Differential Revision: https://reviews.llvm.org/D126921