[Enhancement] Add Scrollable Padding to End of COSMIC Text Editor

[iamkartiknayak]

Cosmic-edit version:

cosmic-edit:
  Installed: 0.1.0~1735575096~24.04~31e135c

Issue/Bug description:
Currently, in the COSMIC Text Editor, the last line of text sticks to the bottom of the editor window. This can make it less convenient to edit or read the last lines of a file. Adding scrollable padding at the end would improve usability by allowing users to scroll past the last line, ensuring it doesn't sit flush with the bottom edge.

Expected behavior:
The user should be able to scroll past the last line of text (e.g., 100px or a similar value) should be added to the bottom of the editor.