Fix some SIMD bugs found by fuzzing

[Robbepop]

• Fixed a bug in i8x16.shuffle translation where it missed a trivial check for reachability.
• Fixed an encoding bug for v128.storeN_lane instructions with offsets that could not be 8-bit encoded.
• Fixed a bug in v128.shift instruction translation with immediate rhs shift amounts.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.21%. Comparing base (2de7c09) to head (abe8cdb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/wasmi/src/engine/translator/simd/mod.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1429   +/-   ##
=======================================
  Coverage   71.21%   71.21%           
=======================================
  Files         161      161           
  Lines       16269    16270    +1     
=======================================
+ Hits        11586    11587    +1     
  Misses       4683     4683           

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