Support touchpad gesture properties in IDC files

Specific touchpads often require small tweaks to the Gestures library's
gesture properties to work well. Examples of such tweaks include palm
thresholds, or the parameters to the stationary wiggle filter. To
support this, allow properties to be set using the 'gestureProp.' prefix
in IDC files, with the spaces in property names replaced by underscores.
For example, to set the "Pressure Calibration Offset" property to 30,
add this line to the relevant IDC file:

    gestureProp.Pressure_Calibration_Offset = 30

Only single-valued boolean, integer, or real properties can be set this
way. There's currently no use case for strings. The only use case for
arrays is for acceleration curves, which wouldn't work well with this
system anyway since they'd be overridden by the pointer speed settings.

Bug: 271251605
Test: atest inputflinger_tests
Test: connect Apple Magic Trackpad 2, check properties are set correctly
      in dumpsys input
Change-Id: I1bf97c9753e48c00d3dc3098cb676f7baebc84ce