[#1675] Add module signatures on hover

Motivation and Context

Problem

Right now there is a (* ... *) placeholder for module signatures on hover. Let's fill it with the right signature.

Solution

Propagate signatures like types inside types pass in the scopes module. Decompile these Ast_typed.signature and use pretty printers to show them to the user.

Related issues

Resolves #1675 (closed) .

✅ Checklist for the LIGO Language Server

• I checked whether I need to update the README.md file for the plugin and did so if necessary:
  • If I implemented a new LSP request, I added it to the list of supported features that may be disabled
  • If I implemented a new LSP method, I added it to the list of supported functionality
• I checked that my changes work in Emacs, Vim, and Visual Studio Code
• (Before merging) The commit history is squashed and prettified, and follows the Serokell commit policy, or the MR is set to squash the commits

Description

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

Added signatures for modules on hovering. They're displayed like:

module Bytes : sig
  val concats : bytes list -> bytes

  val pack : a -> bytes

  val unpack : bytes -> a option

  val length : bytes -> nat

  val concat : bytes -> bytes -> bytes

  val sub : nat -> nat -> bytes -> bytes

end

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).