[JsLIGO]: Add increment & decrement operators (`++` & `--`)

Motivation and Context

The prefix & postfix (increment & decrement) operators (++ && --) were missing in JsLIGO.

These operators are useful in writing for loops

Description

TODOs

• Add grammar & CST nodes
• Add nodes in Ast_unified
• Nanopass
  • Compiler
  • Decompiler
• Add expect tests for compilation & running tests
• Add Unit tests for nanopass (compiler & decompiler)
• Update docs on website

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

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

This MR adds to increment & decrement operators (++ && --) to JsLIGO.

For example

const testIncDec = (() => {
  let inc = 0;
  
  // Prefix increment operator
  assert(++inc == 1);

  // Postfix increment operator
  assert(inc++ == 1);
  assert(inc   == 2);

  let dec = 10;

  // Prefix decrement operator
  assert(--dec == 9);

  // Postfix decrement operator
  assert(dec-- == 9);
  assert(dec   == 8);
})();

Result

$ ligo run test x.jsligo 
Everything at the top-level was executed.
- testIncDec exited with value ().

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).