RangeFinder: Using existing Analog offset for other interfaces (I2C or Serial)

### Feature request
Expand rangefinder offset

**Is your feature request related to a problem? Please describe.**
Need some easy fix to adjust sensor offset.
For example, the Garmin Lidar Lite, has an offset of approx. 25 cm on low range, and users do not have a mean to compensate.

**Describe the solution you'd like**
Just tested using the existing analog offset within this code
https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp#L94

uint16_t _distance_cm = be16toh(val);
float offset = state.offset;
// remove momentary spikes
if (abs(_distance_cm - last_distance_cm) < 100) {
state.distance_cm = (_distance_cm-offset);

**Platform**
[x ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

Start with libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp at the referenced offset handling, then trace the corresponding I2C and Serial rangefinder paths. Confirm how the existing analog offset is represented and where each interface computes distance. Done means users can compensate the sensor offset consistently across the requested interfaces.

Written by the indexing model from the issue text.