Please implement DISTINCT_E_FACTORS

[Jonnie-Cache]

I have the dual extruder and the extruders extrude filament at different rates. By implementing DISTINCT_E_FACTORS, we can set the e-steps (M92) for each tool individually.

[DannyVersluis]

It would be really nice if this was enabled by default. The values ​​for the separate extruders of the dual extrusion head deviate too much to make a decent print without adjusting them properly.

I tried to enable DISTINCT_E_FACTORS, but then it is not possible to compile.
The following messages will then appear:

Marlin/src/inc/SanityCheck.h:1969:38: error: 'X_TO_EN' was not declared in this scope

"DEFAULT_AXIS_STEPS_PER_UNIT has too many elements. (Did you forget to enable DISTINCT_E_FACTORS?)");
"DEFAULT_MAX_FEEDRATE has too many elements. (Did you forget to enable DISTINCT_E_FACTORS?)");
"DEFAULT_MAX_ACCELERATION has too many elements. (Did you forget to enable DISTINCT_E_FACTORS?)");

I tried adding default values ​​for E1, but even then it still doesn't compile.

Please make this work by default.