This patch adds an action to the Kate component that allows the reloading of the syntax highlighting files.
Since I am not very familiar with the codebase I might have overlooked something, especially related to memory management.
Please let me know if I can improve the patch!
Testing
I tested that the reloading works by editing the Markdown syntax highlighting file. After applying a change and reloading the file using the previously set shortcut, the highlighting changed correctly.