Refactor wasmi_core float types: F32, F64

[Robbepop]

For a long time these types didn't know what role they wanted to play.

On the one hand they are meant to be a simple conversion type between u32 and f32 to craft float types that can easily be compared on a bit-wise level. On the other hand they provided a more or less functioning math API. It was never really clear (not even to me) whether one shall use them where possible or avoid them where possible.

With this PR we make all of this clear.

• Both, F32 and F64 are just conversion types.
• All math operations on them have been removed. In order to do math, simply convert them to their respective primitive f32 or f64 type.
• It is still possible to use them as function call parameters where needed but people should use f32 and f64 where possible.
• Their main purpose is to be used in the wasmi::Val enum.
• Outside of their wasmi::Val usage they should be avoided.
• I renamed the file to float.rs to avoid the confusion with NaN canonicalization since those types have nothing to do with it.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 70.43%. Comparing base (9c27ed0) to head (47e05f4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/float.rs	68.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1394      +/-   ##
==========================================
- Coverage   70.43%   70.43%   -0.01%     
==========================================
  Files         156      156              
  Lines       14438    14396      -42     
==========================================
- Hits        10170    10140      -30     
+ Misses       4268     4256      -12     

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