…illcost/prevReg

If we find out that there are no candidates free/busy for refPositions
that need consecutive registers, have at least one range of registers
in the candidates such that allocation is possible.

Intially, we were just returning RBM_NONE if we don't find any freeCandidates,
but instead should try if we can find out if there are any busy candidates
that we should try them out.

…osition

If consecutive registers are being allocated, other refpositions that are live
at the same location might not have enough registers left to be assigned because
all registers are busy. As such, introduce a way to track if we are assigning
at the location of consecutive registers, and if yes, do not take jitstressregs
limit into account.

For consecutive register, also include the register count needed for "minimum
register requirement" when limiting the registers.

With other conditions in place, no need to have LsraLimitFPSetForConsecutive.

…regs