G-code console for LVGL UI

[X-Ryl669]

Description

This is an additional menu for LVGL based UI to allow inputing G-Code directly in the interface and getting answer
It's located in the "More" menu from the "Tool" menu. The flow is like this:

1. Select the G-Code option in the More menu
   
2. Click on "Enter G-Code" and enter your G-Code command
   
3. Upon return, the result of the G-Code command is displayed
   

I don't expect this code to land as-is, but instead request for comments about how to improve it or to better integrate with it.

Requirements

This requires LVGL, and I've based this code above the pending PR #20191.
I hope the former will be merged soon and I think it's better not to append more UI change on this other PR.

Benefits

This opens a lot of possibilities to use your printer without a computer connected to it (in standalone mode). All the features of Marlin are now accessible via the LCD screen (albeit via technical & textual representation) even if a graphical menu is missing to deal with it (for example, getting the current position of all axis is not present by default in LVGL, and this is useful to calibrate a BLTouch sensor).

Configurations

No configuration required. It's enabled by default when LVGL is enabled.

Issues

Currently, as you'll discover, I had to add a hook to the serial's write function to capture the output of a G-Code command.
Looking at the code, there's already some kind of hooking function for ethernet but it's completely non-expandable for third party.
I think Marlin would benefit from a better hooking system (something more generic to capture anything that goes to serial output whatever the serial output selected). Looking at the code, this means either rewriting the SERIAL_CHAR et al. macros so that they can be switched at compile time and/or runtime.

I need to discuss with actual developers what would be the best solution. The solution in this PR is working for MarlinSerial's based on Hardware Serial, but not on USB serial, so it's far from perfect. It's using a pointer to a callback function that can be swapped to a null value to disable/enable hooking at runtime.

Another issue I have is to detect the end of a GCode command's answer. Some command ends with "ok" and I'm currently using this as a sentinel to unhook the serial capture, but I wonder if a signal could be added in the G-code processor to tells any hook that a command has completed processing.

Please let me know what you think, thanks!

[X-Ryl669]

Should be ready now for inclusion...
There is no more the spurious "ok" line anymore 👍

[Valnar8]

I like the idea but I always get a blackscreen after pressing the check mark. I guess that's what you meant with the end detection issue. Even ok didn't help in my case.

However I have some more feedback to this: It's a bit of a pain to enter g-code with this Keyboard layout. Would be a lot better if the standard screen was a num-block, a dot and the most important letters (G, M, X, Y, Z, E and what else are common letters for G-code Parameters)