Settings GUI: Add setting dependencies

[rubenwardy]

Part of #13476

The aim of this PR is to improve User Experience by only showing settings when they make sense. This is currently done in a hardcoded way for shader settings in "Most Used", this PR makes it more generic and will allow removing Most Used in the future.

Settings can have a list of requirements, defined in the settingtypes.txt file. For example:

#    Some example setting description
#
#    Requires: shaders, enable_dynamic_shadows, !touchscreen_gui
example_setting (Example setting) float 0.2 0.001 10.0

These requirements may be:

• The value of a boolean setting, such as enable_dynamic_shadows
• An engine-defined value:
  • shaders (both enable_shaders and a video driver that supports it)
  • desktop
  • android
  • touchscreen_gui for builds with touchscreen controls
  • opengl / gles
• You can negate any requirement by prepending with !

To do

This PR is a Work in Progress

• Hide non-setting components (Ie: "change keys")
• Remove sections with no content
• Remove pages with no content
• Clicking reset on enable_shaders doesn't show settings again
• Trim trailing whitespace
• Show fields as greyed out with a tooltip if it's possible to enable them? Future PR
• Refactor

Question: Should setting and engine-defined keys be distinguished? Perhaps all engine-defined keys should be in capitals - TOUCHSCREEN_GUI, SHADERS, DESKTOP, etc. This may be a good idea for future compat. Say we add a new engine-defined value in the future: foobar. A mod may add this as a requirement in their settingtypes.txt, but this would result in older versions of the engine assuming that it is a setting value not an engine-defined value, and thus showing a warning and considering it not fulfilled. But perhaps its a good thing to have unknown values be unfulfilled

How to test

• Try enabling and disabling shaders. Try various shader options as well

• In check_requirements, add the following to the top to pretend to be Android:

  local TOUCHSCREEN_GUI = true
  local PLATFORM = "Android"

[SmallJoker]

Thanks for the changes. I did a few tests previously and did not find any strange behaviour.