[doc] Reorganize TOC

Motivation and Context

This MR reworks the TOC for easier navigation. It doesn't make any significant changes to the content of pages; it just moves things around to make it easier for developers to find things.

Description

Currently, topics are listed one after the other without grouping things. This MR groups topics according to common programming concepts such as syntax and data types. Here's what the TOC looks like after the MR:

This layout imitates how I've set up docs on docs.tezos.com and the upcoming updates to the SmartPy docs so we're talking about Tezos smart contract languages in a consistent way.

The changes affect only the Next version; I left previous versions the same.

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

Reorganized documentation table of contents

Checklist:

• If a new syntax has been introduced, put a message on slack ligo-lsp
• 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).