Allow motor test mode when reversible motors (3D) enabled

[sensei-hacker]

Needs firmware support for reverse to work

Summary

Fixes the Outputs tab motor test checkbox being disabled when the REVERSIBLE_MOTORS feature (3D mode / bidirectional ESCs) is enabled.

Problem

feature3DSupported was initialized to false and never set to true anywhere. This caused the guard if (self.feature3DEnabled && !self.feature3DSupported) to always block test mode for 3D users. The variable was a leftover from a removed API version check (commit ef831a3 from 2016).

Additionally, a typo (FC.EVERSIBLE_MOTORS instead of FC.REVERSIBLE_MOTORS) in the neutral value sanity check would have caused a runtime TypeError if the code path had been reachable.

Changes

• Removed feature3DSupported variable and the guard that blocked test mode
• Simplified feature3DEnabled && feature3DSupported checks to just feature3DEnabled
• Fixed typo FC.EVERSIBLE_MOTORS → FC.REVERSIBLE_MOTORS
• Improved comment on neutral value sanity check bounds
• Slider initialize to center when reversible mode is on

Testing

• Verified motor test checkbox enables correctly with REVERSIBLE_MOTORS feature active
• Sliders initialize to neutral point (1500) in 3D mode
• Motor values display raw PWM in 3D mode
• Normal (non-3D) motor testing unaffected

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Pikkuboo]

tested on a speedybee f7 v3 fc and motor testing now works when reversible motor is on, but only forwards.

[sensei-hacker]

tested on a speedybee f7 v3 fc and motor testing now works when reversible motor is on, but only forwards.

@Pikkuboo that should be fixed by iNavFlight/inav#11847
I don't suppose you could test it?

[Raffi1202]

Tested the configurator side of this PR (head 660060d) against the bundled 9.1 SITL, driven over CDP:

• Quad X mixer applied, REVERSIBLE_MOTORS enabled in the Outputs tab, saved and rebooted.
• After the reconnect the motor test checkbox is enabled (disabled = false), the four sliders sit at the FC's neutral value (1460 from 3d_neutral) with range 1000-2000 and unlock when test mode is switched on.
• Dragging motor 1 to 1400, 1600 and back to 1500: each value goes out in MSP_SET_MOTOR (bytes 0-1 = 1400 / 1600 / 1500) and MSP_MOTOR reads the same value back; the value label under the slider shows the raw number as expected in 3D mode.
• No renderer exceptions from the tab (only the unrelated dev-mode appGetVersion one on maintenance-9.x).

So the checkbox/slider fix behaves as described. Whether the ESC actually spins backwards below neutral is firmware territory (#11847), which a SITL cannot show.