CLI: add `--skip-generated` in `list-declarations` sub-command

Motivation and Context

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

A new flag for info list-declarations allows to prevent printing the generated $main entrypoint:

$ cat b.jsligo 
type storage = int;

type ret = [list<operation>, storage];

@entry
const increment = (delta: int, store: storage): ret => [list([]), store + delta];

@entry
const decrement = (delta: int, store: storage): ret => [list([]), store - delta];

@entry
const reset = (_: unit, _: storage): ret => [list([]), 0];
$ ligo info list-declaration --display-format dev --only-ep --skip-generated b.jsligo
b.jsligo declarations:                   
reset
decrement
increment

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).