Fix compilation for negative integers

Motivation and Context

It was reported in issue #1506 that pushing negative number onto the stack emit NEG

Fixes #1506

Description

This MR adds a peephole optimization in self_michelson, that checks for such patterns like PUSH int 100 ; NEG and turns them into PUSH int -100

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

Improves the Michelson compilation for negative integers, removes the unnecessary NEG instruction in the case of negative integers

Before:

$ ligo.55 compile expression cameligo ' -100' --without-run
{ PUSH int 100 ; NEG }

After

$ ligo compile expression cameligo ' -100' --without-run
{ PUSH int -100 }

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).