- The `sdcard.transfer_port` variable is Marlin's internal serial port index, not the physical serial port number.
- Added packet number to "ok" response so hosts don't need to wait for the ACK.
- Renamed feature to `BINARY_FILE_TRANSFER`, as the speed up is only consequential to the ability to transfer binaries over serial.

Reference #13250

Ticket #13228

If `INCH_MODE_SUPPORT` is undefined, G20 is an unknown command as it should be (Marlin is, by default, operating in metric mode). G21, however, is found in many slicers and printer start gcode sections and should be accepted (as a NOOP) to avoid the unknown commands.

Co-Authored-By: shitcreek <45380455+shitcreek@users.noreply.github.com>

Fix #13184

- Turn off bed leveling prior to calibrating.
    - This prevents lateral probes from having a Z component that
      triggers the Z endstop and causes the motion to be aborted.
- Got rid of static const float arrays "dimension" and "true_center"
    - Frees up 24 bytes of SRAM
- Changed incorrect use of "bool" for float in backlash macros.
    - Replaced arguments with 0.0f and 1.0f for clarity.
- Now only disables soft endstops (since calibration cube is outside of bed)
    - Not necessary to disable global endstops

Apply minimum `C` in `M303`. `PID_autotune()` needs to be called with a 'C'ycles-parameter >2 to give meaningful (different from 0) PID-factors. Therefore silently raise C to 3. Fixing one aspect of #13104