This method will track if the defs/uses are live at the same location as
where the consecutive registers were allocated. If yes, it will skip the
constraint imposition on it during JitStressRegs

When we have copyReg that was just restored or previously assigned
to a different register, also track it as live at the location so
it doesn't get allocated again for different refposition at the same
location.

…isters

Under JitStressRegs, there are multiple ways in which consecutive registers demand
cannot be met. So skip restricting the registers for `registerAssignment` of a refPosition
(which are allowable candidates that can be assigned to the given refposition). Instead
limit the free registers to alternate under stress mode, so we can verify the code if it
can handle situation where it needs to pick from a mix of free/busy registers.