x64: Implement SIMD fma (#4474)

* x64: Add VEX Instruction Encoder

This uses a similar builder pattern to the EVEX Encoder.
Does not yet support memory accesses.

* x64: Add FMA Flag

* x64: Implement SIMD `fma`

* x64: Use 4 register Vex Inst

* x64: Reorder VEX pretty print args

crates/fuzzing/src/generators/codegen_settings.rs

@@ -111,6 +111,7 @@ impl<'a> Arbitrary<'a> for CodegenSettings {
                     std:"popcnt" => clif:"has_popcnt",
                     std:"avx" => clif:"has_avx",
                     std:"avx2" => clif:"has_avx2",
+                    std:"fma" => clif:"has_fma",
                     std:"bmi1" => clif:"has_bmi1",
                     std:"bmi2" => clif:"has_bmi2",
                     std:"lzcnt" => clif:"has_lzcnt",