Set Key Mapper as the device assistant to trigger key maps

[sds100]

Developer TODO (don't remove)

• create new branch. put issue number at start of name
• update documentation with how the gradle modules and build variants are set up.
• Add strings to Crowdin.
• Implement voice assistant trigger
• When selecting the assistant trigger, show a Compose dialog explaining what the different types are and let them choose any, voice or device.
• Show error if key mapper is not chosen as the device assistant trigger (Only show if the feature is purchased, otherwise show an error that this key map will not work until they purchase the feature)
• Do not crash if the AssistantTrigger doesn't exist when importing assistant key maps to the FOSS version.
• Create icon for the assistant activity.
• Hide button for trigger key options in assistant trigger key list item
• Do not allow a parallel trigger with multiple assistant keys.
• Do not allow long press assistant keys.
• Does the new Trigger UI work when showing Trigger + Actions on same screen.
• Have a button next to "Record trigger" button that is for "Advanced triggers"
• Send a notification advertising the new feature because it could add a 3rd button to remap.
• Disable the Device Assistant activity in manifest if they haven't purchased it.
• Write guide on website and link it to help button when configuring.
• Show thank you dialog after purchasing.
• Advertise it supporting Bixby, Google Assistant, Active Edge etc.
• Test using this feature in games and when screen is off.
• Disable the device assistant activity unless they have paid
• merge and delete branch (don't squash because want commit history to see why I made changes)

To support the future maintenance of Key Mapper, this feature will be paid and closed-source. This will be a small feature to test this method of financial support for the project. Patches and smaller features in the core Key Mapper app will remain FOSS. The F-droid build will not contain this feature or depend on the libraries incompatible with F-droid such as the Google Play Billing Library.