fix(telemetry): Inconsistent/wrong GPS distance calculation

[mha1]

fixes #4437

PR #4250 introduced a mechanism to allow a value widget to detect a change in GPS position. This was realized by storing a hash value in the value variable of class TelemetryItem. Unfortunately value is defined in a union together with a placeholder for distFromEarthAxis.

class TelemetryItem
{
  public:
    union {
      int32_t  value;           // value, stored as uint32_t but interpreted accordingly to type
      uint32_t distFromEarthAxis;
    };
...

By writing the hash for the changed lat/lon to value the calculated distFromEarthAxis is overwritten. In case a calculated telemetry sensor "distance" is defined this leads to a wrong calculation of the distance between craft and home point.

Changes:

• separated and moved storage of distFromEarthAxis to class TelemetryItem's gps struct to prevent overwriting distFromEarthAxis. This should not affect RAM usage due to the way the gps struct is embedded in a union for other types of data (cells struct is still larger).
• changed distFromEarthAxis to pilotDistFromEarthAxis to align variable name with pilotLatitude and pilotLongitude

Tested using the procedure described in #4437

[mha1]

tested on 2.9.2 and current main:

• value widget updating GPS position ok
• calculation of GPS distance ok

[pfeerick]

Will this cherrypick into 2.9 without any conflicts? If so, you can have it for 2.9.3 ;)

[mha1]

Will this cherrypick into 2.9 without any conflicts? If so, you can have it for 2.9.3 ;)

yes sir