Infer REX prefix for SIMD store and vconst instructions

[abrown]

• This has been discussed in issues #1090 and #1379.
• A short description of what this does, why it is needed: this demonstrates inferring REX prefixes for SIMD store and vconst instructions; if we think this is the right direction, we have some additional to do to infer REX prefixes for the following recipes:

enc_32_64: fstDisp8, fstDisp32, fld, fldDisp8, fldDisp32, fspillSib32, fregspill32, ffillSib32, fregfill32, frmov, furm, fa, fax, f_ib
enc_32_64_maybe_isap: r_ib_unsigned_r, fa_ib, fa, r_ib_unsigned_gpr, fcmp, icscc_fpr
enc_both: frurm, pfcmp, fa, furm

• This PR contains test cases, if meaningful.
• A reviewer from the core maintainer team has been assigned for this PR.

[iximeow]

I have the above question, but I'm not sure if I'm misreading, or there's actually a bug, so I'm not explicitly requesting changes.. this looks good overall, but I'm particularly curious if this gets something like mov xmm1, [r11] right. That's the only case (base reg is the only one requiring REX prefix) that I think warrants a closer look.

[iximeow]

🎉

[iximeow]

Thank you! I'll approve but want an explicitly acknowledgement you're g2g before hitting merge :)

[abrown]

I think we're good-to-go. I'm not really looking forward to doing this same thing for 20+ other recipes so any suggestions are appreciated. The "size_plus_maybe_sib_or_offset_for_inreg_0_plus_rex_prefix_for_inreg0_outreg0" code is not code I would hope to make a career of... is there another way?

[abrown]

...and by "good-to-go" I mean I ran this change with the wasmtime tests (latest on master) and everything passed except some wasm_c_examples for unrelated reasons like make: *** No rule to make target 'wasm-c-api/out/example/reflect-c'