Upgrade the Code Editor to use CodeMirror 6 and revamp the editor theme

[kevjt]

Background

Upgrading the CodeMirror dependency will provide several additional benefits besides making the YAML indentation marker possible:

• CodeMirror 6 is structured in a more extensible way and allows users to define more of their own plugins. There may be other use-cases we will need this for in the future.
• Customisation of the code editor theme (colour palette for syntax highlighting) can be done directly in .tsx code with CodeMirror 6
• CodeMirror 5 is no longer being actively maintained.

The aim of this PR is to keep the functionality largely the same as it was before, with no noticeable difference besides the colour palette for the syntax highlighting.

Theme update

This update brings new colours to syntax highlighting in the editor. The new "Github" theme colours are shown below in the comparisons. The goal here was to improve the distinction between various parts of the language syntax, especially in the case of the light theme for YAML where it was previously hard to distinguish some parts.

[octoreleasebot]

Release Note: Upgrade CodeMirror from v5 to v6 and apply new code editor theme for better syntax highlighting

[Octobob]

:tada: The fix for this issue has been released in:

Release stream	Release
2024.3	2024.3.3492
2024.4+	all releases