Restore necessary and needed loop termination logic.

…to fit more code on the screen and correct outdated commentary contrasting ABL.

* Automatically reset stepper timeout in manage_inactivity

Any code that adds moves to the planner can skip resetting the stepper timeout. We can let `idle` / `manage_inactivity` reset the timer whenever it detects any moves in the planner.

* blocks_queued => has_blocks_queued

Some probes don't work near the edges of the bed. This change promotes MIN_PROBE_EDGE to a general setting that applies to all probing functions.

Some "fix-mounted" probes need manual stowing. And after probing some may prefer to raise or lower the nozzle. This restores an old option but tailors it to allow raise or lower as preferred.

Reference #9983

75ms might  be excessive...    But I know people are seeing problems with PronterFace as the client...

`ENABLED` only works for flag-type options. Floats must use `#ifdef`.

* Work around for serial buffer over run

PronterFace sends a lot of M105 commands.  During long operations such
as UBL's G29 P1, G29 P2, G29 P4 and G26 this can over run the serial
buffer.   This results (very often) in a M1 (actually a M1M105) ending
up in the command queue.

Until we figure out a better way to resolve this issue, this will keep
the UBL commands from experiencing bogus commands at thier completion.

Give PronterFace time to print the UBL What information...

A number of regressions were patched also. The UBL G29 P2 and P4 Press and Hold had stopped working. It is very possible this is broken in the bugfix_v1.1.x branch also.

The main purpose of the Pull Request is to get the 3-Point mesh tilting to use the LSF algorithm just like the grid based mesh tilt. This simplifies the logic and reduces the code size some what. But the real reason to do it is the 3-Point case can be solved exactly. And by feeding these numbers into the LSF algorithm it provides a way to check all that code for 'correctness'.