This fixes emitGetVexPrefixSize to support detecting 2-byte prefix support (#79478)
* Remove the dead emitOutputRexOrVexPrefixIfNeeded and rename emitOutputSimdPrefixIfNeeded to emitOutputRexOrSimdPrefixIfNeeded
* Remove the dead emitGetAdjustedSize and rename emitGetAdjustedSizeEvexAware to emitGetAdjustedSize
* Simplify the emitGetEvexPrefixSize and emitGetVexPrefixSize methods
* Create helper emitExtractVexPrefix and emitExtractEvexPrefix functions
* Update emitGetVexPrefixSize and emitGetEvexPrefixSize to take an instrDesc
* Update emitGetPrefixSize to take the instrDesc so the VEX prefix size can be computed correctly
* Update emitGetVexPrefixSize to support returning 2 or 3
* Ensure IF_RWR_CNS is handled in emitGetVexPrefixSize
* Don't try to estimate the 2-byte VEX prefix when optimizations are disabled
* Ensure we don't negatively impact estimated alignment sizes for debug code
* Just check MinOpts not OptimizationsDisabled
* Mark some of the modified methods as const to indicate they don't mutate the emitter
* Resolve the throughput issue by not getting optSize untill necessary
* Switch back to doing accurate vex prefix size estimation always
* Small cleanup to reduce regression