* [New Feature] I2C position encoder support

I plan to continue improving/cleaning this up, as there areas that need work.

* let the cleanups begin.

* progress

* more progress

* comments, rename files, etc.

* clean

* Cleanups per thinkyhead

* a few more cleanups

* cleanups, bugfixes, etc.

* remove unnecessary passes_test(), additional cleanups/optimizations

* cleanups

* misc.

* Fix up I2CPEM.init() and a few other things.

* organize, fix, rename, etc.

* more optimization

* a few more tweaks

only seen if

#if ENABLED(TEMPERATURE_UNITS_SUPPORT)
      ...
    #if
ENABLED(ULTIPANEL) && DISABLED(DISABLE_M503)

invalid conversion from 'const char*' to 'char*' [-fpermissive]