Preserve exact x87 64-bit integer transfers in reduced precision

Reduced-precision x87 load/store sequences round 64-bit integer payloads. Preserve exact integer transfers through unchanged stack values and across block boundaries. Keep the current iOS host-addressed memory accesses.

Adapted from the Playport authors at https://github.com/playportdev/playport/tree/412de5f8c0bdd26d84e0127eb5776ba992e3b152/patches/fex. Attribution is in docs/playport-port.md. This is independent of the upcoming BCD app port.

Validation: IR generation and ARM64EC compilation of the x87 IR pass and opcode dispatcher passed. Included the original same-block and cross-block assembly regressions; these still require a FEX test host to execute.

Draft: no fresh device or gameplay proof. Madeira must update its component pin to use this change.