Fix OSD throttle position element calculation and add 3D support

Previously the Throttle Position element calculation was based solely on the raw rcCommand value and didn't take into account the min_check deadzone so the resulting displayed percentage was incorrect. Also 3D trottle handling was not considered.

Corrected the calculation and added support for 3D throttle modes. Reversed thrust will be represented with negative throttle percentages.

src/test/unit/osd_unittest.cc

@@ -1079,4 +1079,5 @@ extern "C" {
     bool pidOsdAntiGravityActive(void) { return false; }
     bool failsafeIsActive(void) { return false; }
     bool gpsRescueIsConfigured(void) { return false; }
+    int8_t calculateThrottlePercent(void) { return 0; }
 }