[2.0.x] option to enable firmware retraction but disable autoretract

[Palatis]

Description

add a configuration_adv.h option to enable firmware retraction but disable auto-retract.
auto-retract will stay off (ignores M209) and firmware retraction can only be issued by G10 and G11.

Benefits

saves ~500 bytes of PROGMEM on AVR when auto-retract is disabled.

[Palatis]

should have the indentation corrected

[thinkyhead]

Should be #if ENABLED(...)

[thinkyhead]

It would be better to disable M209 completely, so the G-code throws an “unknown G-code” error when this feature is not enabled.

[Palatis]

weird... why does travis fail?
I can compile over here.

[thinkyhead]

Travis tests a large number of configuration options. Some of them will pass, others will fail. In this case the error was a simple typo in configuration_store.cpp.

[thinkyhead]

When the code has been rebased, as we do here in Marlin-land, you must not force-push your branch or you end up destroying all the corrections we've made.

I've added a single commit containing all the changes that your last force-push stomped on. Check it out. It's instructive.

In future, please ask for guidance before force-pushing any changes to an open PR.

[Palatis]

I'm really sorry about the force-push, as described in #11869.

I'll see what I can do and tweak the script, finally push by hand to avoid breaking anything.

Apologize again for the inconvenience.