LayerSwitcher: Add scroll to Quick Access Presets view

[linusfj]

Describe the bug
The Quick Access Presets view in the LayerSwitcher doesn't support scrolling, making it impossible to access presets that extend beyond the visible area.

Steps to reproduce
Steps to reproduce the behavior:

1. Open the LayerSwitcher
2. Navigate to the Quick Access Presets view
3. Change the size of the LayerSwitcher plugin window
4. Observe that there's no scroll functionality to access the additional presets

Expected behavior
The presets list should be scrollable when content overflows.