feat(gnovm): add software floating point package

[thehowl]

Based on the runtime softfloat64.go file.

Fixes #312 .

Still WIP, need to include it into the source code for the GnoVM.

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

Attention: Patch coverage is 67.30310% with 137 lines in your changes missing coverage. Please review.

Project coverage is 60.94%. Comparing base (1e27785) to head (aa07dce).
Report is 87 commits behind head on master.

Files with missing lines	Patch %	Lines
.../gnolang/internal/softfloat/runtime_softfloat64.go	70.72%	108 Missing and 5 partials ⚠️
gnovm/pkg/gnolang/internal/softfloat/softfloat.go	27.27%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2863      +/-   ##
==========================================
+ Coverage   60.91%   60.94%   +0.03%     
==========================================
  Files         564      566       +2     
  Lines       75273    75692     +419     
==========================================
+ Hits        45856    46134     +278     
- Misses      26046    26183     +137     
- Partials     3371     3375       +4     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (-0.86%)	⬇️
gno.land	67.17% <ø> (ø)
gnovm	65.80% <67.30%> (+0.02%)	⬆️
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.08% <ø> (-0.01%)	⬇️

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