TouchControls: Implement an option for dig/place buttons

[grorp]

meant to resolve #13229

This PR adds the option to have dig/place buttons as a part of the touchscreen layout, instead of using long/short tap gestures for digging/placing. The biggest advantage is probably that the buttons allow for precise timing.

This PR introduces three different "modes" for the touch controls (new setting touch_interaction_style):

• "Tap" (previously touch_use_crosshair = false)
  Long/short tap anywhere on the screen to interact. Interaction happens at finger position.
• "Tap with crosshair" (previously touch_use_crosshair = true)
  Long/short tap anywhere on the screen to interact. Interaction happens at crosshair position.
• "Buttons with crosshair" (NEW)
  Use dedicated dig/place buttons to interact. Interaction happens at crosshair position.

Adding an option for dig/place buttons and framing the different control schemes as "modes" (as an enumeration) in the settings was inspired by Minecraft's mobile version.

Video demo of the three modes (the new mode is at the end):

buttonn.mp4

To do

This PR is a Ready for Review.

Note: ~300 of the ~530 added lines in this PR are the new SVG icons.

How to test

• Test the different modes, confirm that they work as expected.
• Try upgrading from an earlier Luanti version, confirm that settings are preserved, confirm that the new mode still works as expected.
• Confirm that dig/place buttons don't appear in modes other than "Buttons with crosshair".
• Confirm that custom dig/place button positions aren't lost when switching away from "Buttons with crosshair" mode and going back later.

To have some fun, you could try the new control scheme in Block League on the A.E.S. server