Make idSmallCns signed to allow including -1 (#87373)

* Make idSmallCns signed on xarch

* Ensure EMITTER_STATS are correctly tracked

* Use signed _idSmallCns on other platforms as well

* Have EMITTER_STATS track additional information about constants

* Also track whether the constant fits into 8, 16, or 32-bits

* Fix the formatting/ordering of the EMITTER_STATS header

* Ensure the EMITTER_STATS header covers all the instrDesc types

* Ensure that instrDesc counts are all being tracked by EMITTER_STATS

* Apply suggestions from code review

Co-authored-by: Bruce Forstall <brucefo@microsoft.com>

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Co-authored-by: Bruce Forstall <brucefo@microsoft.com>

Author: tannergooding