TenBrushes: Add an option to automatically select freehand brush tool when using a brush shortcut

This merge request changes three things:

• Adds a checkbox option to TenBrushes that, when enabled, automatically selects the freehand brush tool when using one of the preset shortcuts. Off by default.
• Fixes a typo in a38a33c7 so that the dropbutton issue is fixed properly.
• Fixes the floating message call so that the floating message appears when using any document rather than the first indexed document.

Test Plan

• Observe behavior with option off, enable the new option, select a different tool, press one of the brush preset shortcuts, and observe new behavior.
• Select a preset box without a brush selected.
• Observe floating message while using the brush shortcuts on any particular document/view, and not just the first document/view.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.