Stdlib: list updating functions

Motivation and Context

It can be useful to have new functions updating lists.

Description

This MR adds new functions for updating lists.

We also add find_opt reference in documentation that was missing.

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

New functions in stdlib's List module:

• val filter_map : ('a -> 'b option) -> 'a list -> 'b list
• val update : ('a -> 'a option) -> 'a list -> 'a list
• val update_with : ('a -> 'a option) -> 'a -> 'a list -> 'a list

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).