JsLIGO: list concatenation helper

Motivation and Context

It was Benjamin's suggestion to add a way of writing list concatenation in JsLIGO.

Description

We add support for it as list([...xs, ...ys]).

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

Introduce a new way of doing list concatenation in JsLIGO:

const xs = list([1, 2, 3]);
const ys = list([4, 5]);
const zs = list([...xs, ...ys]);

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).