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CC.@lewing@BrzVlad

This is triggering a mono-runtime assert for wasm and impacts the generic math API surface we want to preview at build.

Worked around some test failures (and logged corresponding issues). Also fixed an error where these APIs shouldn't be on float/double/decimal/Half. The floating-point types are getting separate APIs to get the exponent and significand instead, so that the value can be understood.

No changes, just squashed commits together and rebased ontop of#68043 now that it's merged.

This is now "just" theGetShortestBitLength,GetByteCount, andWriteLittleEndian APIs + relevant tests and doesn't include the WASM disablement since#67999 repros even with them disabled

Merge with main to pickup#68058