Refactor Wasmi translator register visitation (#1178)

* refactor visit registers

This simplifies integration of the planned wasmi_ir crate.

* improve and apply rustfmt

.rustfmt.toml

@@ -1,3 +1,4 @@
 imports_granularity = "Crate"
 imports_layout = "HorizontalVertical"
 edition = "2021"
+match_arm_leading_pipes = "Preserve"

crates/wasmi/src/engine/bytecode/mod.rs

@@ -1,6 +1,7 @@
 mod construct;
 mod immediate;
 mod utils;
+mod visit_regs;
 
 #[cfg(test)]
 mod tests;
@@ -30,6 +31,7 @@ pub use self::{
         Sign,
         Table,
     },
+    visit_regs::VisitRegs,
 };
 use crate::{core::TrapCode, engine::EngineFunc, Error};
 use core::num::{NonZeroI32, NonZeroI64, NonZeroU32, NonZeroU64};