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.

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 ⚠️

📢 Thoughts on this report? Let us know!

[thehowl]

Superseded by #3185