Fixed MeshEditor menu

[digant73]

BUGFIXES:

• Fixed other bugs introduced by Mesh Editor - Overhaul #2737:
  • wrong column index used for both SetMeshValue and MeshTuner
  • wrong color gradients applied after changing a mesh with MeshTuner
  • missing save popup in some situations
  • broken navigation panel (no more possible to use the rotary encoder to navigate on mesh values)
  • etc...
• Fixed other bugs introduced by Leveling points bugfix #2713 (previously fixed by Fixed bug in L Corner menu #2525)
• Minor cleanup: removed unneeded function declarations on some .h files

@bigtreetech: As you can understand, I'm very tired and not going to waste other time in the future for fixing something that was perfectly working and not needing any rework (no bug reported in years), especially when the code was originally made by me. I'm sure this takes away useless time also to you for managing/reviewing unneeded/useless PRs. For any other bug introduced by some contributors affected by an outstanding ego I will simply revert entirely to previous code. I will also avoid to provide specific details about the code logic and the fixed bugs just to avoid to tease the extraordinary fancy such as the soap opera (a never ending story) reported in #2776 (e.g. infoMachineSettings.firmwareType == FW_MARLIN here, infoMachineSettings.firmwareType != FW_REPRAPFW immediately after, the 10th broken rework of the VFS API (that is properly and perfectly working), the restore of broken strncpy versions (with fantasy names and a new "smart" coding style based on logical(/bit operators such as "n -= !!n")) causing wrong navigation on print file selection, the 100th rework of fan/heat/speed/extrude and so on). Thank you for your understanding.

fixes #2782

PR STATE: Ready for merge