And reduce the function size to simplify

・Update forgotten Configuration_adv.h of Felix\DUAL and K8400\Dual-head

・Make descriptions the same as others

.. and give the hint to try lower values if possible.

Simply apply enabled settings instead of requiring users to edit
stepper_indirection.cpp

- Fix typos, verbiage
- Fix naming of `setup_endstop_interrupts`
- Some formatting, indentation, spacing

Configuration.h: back in sync, new features configured
Configuration_adv.h: back in sync, new features configured
README.md: text updated

If ENDSTOP_INTERRUPTS_FEATURE is enabled this tries to set up interrupt routines
for all used endstop pins. If this worked without errors, `endstops.update()` is called
only if one of the endstops changed its state.

The new interrupt routines do not really check the endstops and react upon them. All what they
do, is to set a flag if it makes sense to call the endstop test we are used to.

This can be used on:
* ARM (DUE) based boards - all pins can raise interrupts,
* RAMPS - all 6 endstop pins plus some other on EXT-2 can raise interrupts,
* RAMPS based boards - as long the designers did not change the pins for the endstops or at least left enough,
* all boards, if there are enough pins that can raise interrupts, and you are willing/able to swap with pins dedicated to other purpose.

・Update forgotten K8400\Dual-head\Configuration.h
・Adjust spacing

implemented G-Code M355 into Marlin

As pointed out by #5044

About Configuration.h:
・Fix the PR #4899 (ABL: Enable by type. Bilinear for all.)
Remove Duplicated contents

・Fix the PR #4305 (Custom boot screen feature improvement)
Revert from "during boot" to "during bootup" in all the example
Configuration.h

・Fix the PR #4207 (Clean up, simplify and generalize the Allen-key-probe
code.)
Resolve and relocate the duplicated definitions in Z_PROBE_ALLEN_KEY
section

・Follow-up the PR #4805 (Additional documentation of Configuration.h)
Add forgotten changes to all the example Configuration.h

Adjust spacing

About Configuration_adv.h:
Add missing description of SLOWDOWN for DELTA

Adjust spacing