Remove unnecessary extend instructions

[Robbepop]

The Wasm i64_extend_i32_u and i64_extend_i32_s instructions are unnecessary in Wasmi bytecode.

• The i64_extend_i32_u instruction is essentially a no-op in an untyped bytecode.
• The i64_extend_i32_s instruction can be replaced by the i64_extend32_s instruction since Wasmi bytecode is untyped and the only difference between these two instructions is their effect on the type system.

Technically the i32_wrap_i64 x instruction could be replaced by i64.and x 0xFFFF_FFFF but due to Wasmi's current bytecode encoding this replacement representation would require substantially more encoding space and was less efficient.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.80%. Comparing base (0a6a083) to head (9f90837).

Files	Patch %	Lines
crates/wasmi/src/engine/translator/mod.rs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1147      +/-   ##
==========================================
+ Coverage   79.78%   79.80%   +0.01%     
==========================================
  Files         296      296              
  Lines       25422    25424       +2     
==========================================
+ Hits        20284    20289       +5     
+ Misses       5138     5135       -3     

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