Cursor color setting for edit mode

### ⚠️ This issue respects the following points: ⚠️

- [x] This is a **enhancement/feature request**. Not a [bug or question](https://github.com/gsantner/markor/issues/new/choose).
- [x] The topic is **not** already reported at [Issues](https://github.com/gsantner/markor/issues?q=#js-issues-search). _(I've searched it and checked most recent issues)_.
- [x] Markor **is** up to date. See [Releases](https://github.com/gsantner/markor/tags) for the latest version. Updates are available from [F-Droid](https://f-droid.org/en/packages/net.gsantner.markor/) and GitHub.
- [x] The wanted feature/enhancement is not present in the latest development version (git master). (Please [download](https://nightly.link/gsantner/markor/workflows/build-android-project/master) and try the test version of Markor, named **Marder**. Don't worry; Markor and Marder appear as completely separate applications. You can install both side-by-side, and Markor's settings are not touched. If your desired feature is present, you don't need to open this issue. The change will be part of the next Markor update.)

### Description

Thanks for the amazing work!

The color settings support background and foreground color. In order to map more closely to color themes, I'd appreciate if it also supported the cursor color in edit mode.

### Information

-

### Source

F-Droid

### Format / File type

Markdown

### Additional info / Log

```shell

```

Start by tracing the existing background and foreground color settings for edit mode in the Android app, then inspect how the editor renders its cursor. Done means users can configure a cursor color alongside the existing color settings and see it applied in edit mode.

Written by the indexing model from the issue text.