feat: make it possible to create a custom Markdown code theme

[ndonkoHenri]

Fixes #4342

Code

import flet as ft

def main(page: ft.Page):
    data = """
## Code blocks

```python
class MyClass(object):
    def __init__(self):
        pass
        
    def greet(self):
        print("Hello World")
    """

    page.add(
        ft.Markdown(
            data,
            extension_set=ft.MarkdownExtensionSet.GITHUB_WEB,
            # code_theme=ft.MarkdownCodeTheme.ATOM_ONE_DARK,
            code_theme=ft.MarkdownCustomCodeTheme(
                keyword=ft.TextStyle(color=ft.colors.RED),
                comment=ft.TextStyle(color=ft.colors.GREY_300),
                class_name=ft.TextStyle(
                    size=17,
                    color=ft.colors.BLUE,
                    weight=ft.FontWeight.BOLD,
                ),
                function=ft.TextStyle(color=ft.colors.YELLOW),
                string=ft.TextStyle(color=ft.colors.GREEN),
                variable=ft.TextStyle(color=ft.colors.PINK),
            ),
        )
    )


ft.app(main)

Summary by Sourcery

Add support for custom Markdown code themes, allowing users to define their own styles for code elements. Update the Markdown control to accept both predefined and custom themes, and enhance the theme parsing logic to handle custom theme definitions.

New Features:

• Introduce the ability to create a custom Markdown code theme by adding a new class MarkdownCustomCodeTheme that allows users to define custom styles for various code elements.

Enhancements:

• Enhance the Markdown control to support both predefined and custom code themes by updating the code_theme parameter to accept either MarkdownCodeTheme or MarkdownCustomCodeTheme.
• Improve the parsing of Markdown code themes by adding a new function parseMarkdownCodeTheme to handle both string and JSON inputs, allowing for more flexible theme definitions.