- New STM32 env for Creality V4 boards.
- Separate Libmaple targets into their own `ini` file.
- Temporarily remove unusable targets from `pins.h`.

Co-authored-by: ellensp <ellensp@hotmsil.com>
Co-authored-by: Scott Lahteine <github@thinkyhead.com>

Fix #21928

* Consolidate variant scripts
* Rename Marlin-local boards
* Simplify variants where possible
* Rename variants
* CHITU_F103 and MEEB_3DP: Maple platform `platformio-build-stm32f1.py` uses the 'board' name, not 'board_build.variant' so folder names match 'board' and not `board_build.variant`.