[android] Enable OnePlus middle click workaround

Turns F21 into middle click presses because their stylus is weird. Enabled unconditionally for now because a setting requires text changes and it's pretty unlikely for users to care about F21.

Only cherry-pick the first of these commits to 6.0!

Test Plan

• Open the tablet preferences, look that there's a new checkbox.
• Have a OnePlus tablet and check whether the stylus button inputs a middle click or F21, depending on if the workaround is enabled or not.

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.
• Does the patch add a user-visible feature? If yes, is there a documentation MR ready for it at Krita Documentation Repository?

Reminder: the reviewer is responsible for merging the patch, this is to ensure at the least two people can build the patch. In case a patch breaks the build, both the author and the reviewer should be contacted to fix the build. If this is not possible, the commits shall be reverted, and a notification with the reasoning and any relevant logs shall be sent to the mailing list, kimageshop@kde.org.