PreArm allow Re-Arm (without resetting PreArm AUX)

[nerdCopter]

• Arming still requires PreArm switch.
• set prearm_allow_rearm = ON, default is OFF.
• This allows re-arming mid-air, still requiring preArm, but without need for PreArm AUX resetting.
• TESTED SUCCESSFUL
• Required for mid-air rearm: set small_angle = 180 (when using ACC)
• WARNING - it is very hard to coordinate 0 throttle (required for arming) in mid-air.

originally on Betaflight PR betaflight/betaflight#14013

[nerdCopter]

$ grep -Iirn prearm_allow_rearm src/
src/main/interface/settings.c:829:    { "prearm_allow_rearm",         VAR_UINT8  | MASTER_VALUE | MODE_LOOKUP, .config.lookup = { TABLE_OFF_ON }, PG_ARMING_CONFIG, offsetof(armingConfig_t, prearm_allow_rearm) },
src/main/fc/rc_controls.h:152:    uint8_t prearm_allow_rearm;             // allow re-arming without need to reset the preArm AUX channel
src/main/fc/rc_controls.c:90:                  .prearm_allow_rearm = 0,
src/main/fc/fc_core.c:228:            if (IS_RC_MODE_ACTIVE(BOXPREARM) && (!ARMING_FLAG(WAS_ARMED_WITH_PREARM) || armingConfig()->prearm_allow_rearm)) {

Codacy reported: struct member 'armingConfig_s::prearm_allow_rearm' is never used.

The Codacy report is incorrect.

• if (IS_RC_MODE_ACTIVE(BOXPREARM) && (!ARMING_FLAG(WAS_ARMED_WITH_PREARM) || armingConfig()->prearm_allow_rearm)) {

  In this line, armingConfig()->prearm_allow_rearm is read and evaluated as part of a boolean expression, which constitutes a direct use of the struct member.

[nerdCopter]

Checked by two different AI's as good. merging.