Implement codegen_texture_fetch() and TMU combine paths for ARM64:
- Perspective-correct W division using SDIV (replaces x86 IDIV)
- LOD calculation via CLZ (replaces BSR, inverted: 63-CLZ)
- Point-sampled texture lookup with clamp/wrap S/T
- Bilinear filtered 4-tap blend using NEON (UXTL+MUL+ADD+EXT+USHR+SQXTUN)
- Mirror S/T via TBZ+MVN (replaces TEST+JZ+NOT)
- TMU0-only, TMU1-passthrough, and dual-TMU combine paths
- Dual-TMU tc_mselect/tc_add/tc_invert for RGB + tca_* for alpha
- trexInit1 override path
- Upstream bug at x86 line 1303 (0x8E) NOT ported — correct ADD used

Bug fixes discovered during review:
- Bilinear LDR D addressing: added LSL w4, w4, #2 before 64-bit texel
  pair loads to convert texel index to byte offset (ARM64 LDR Dt has no
  LSL #2 option, unlike x86 MOVQ with *4 scaling)
- LOD mantissa shift: changed LSR_REG to LSR_REG_X (64-bit) since the
  W reciprocal after LSL #8 can exceed 32 bits
- AND_BITMASK for 0xF0 mask: corrected from (N=0,immr=24,imms=27) which
  was an invalid encoding to (N=0,immr=28,imms=3) per ARM64 logical
  immediate rules
- Added #include <stddef.h> for offsetof() in _Static_assert checks