Support for MEEB 3DP board (#18138)

Marlin/src/core/boards.h

Marlin/src/pins/pins.h

Marlin/src/pins/stm32f1/pins_CCROBOT_MEEB_3DP.h

buildroot/share/PlatformIO/boards/MEEB_3DP.json

buildroot/share/PlatformIO/ldscripts/STM32F103RC_MEEB_3DP.ld

buildroot/share/PlatformIO/scripts/STM32F103RC_MEEB_3DP.py

...PlatformIO/scripts/STM32F103RC_MEEB_3DP_create_variant.py

buildroot/share/PlatformIO/variants/MEEB_3DP/board.cpp

buildroot/share/PlatformIO/variants/MEEB_3DP/board/board.h

...droot/share/PlatformIO/variants/MEEB_3DP/ld/bootloader.ld

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/common.inc

...root/share/PlatformIO/variants/MEEB_3DP/ld/extra_libs.inc

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/flash.ld

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/jtag.ld

...droot/share/PlatformIO/variants/MEEB_3DP/ld/mem-flash.inc

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/mem-jtag.inc

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/mem-ram.inc

buildroot/share/PlatformIO/variants/MEEB_3DP/ld/ram.ld

...root/share/PlatformIO/variants/MEEB_3DP/ld/stm32f103rb.ld

...PlatformIO/variants/MEEB_3DP/ld/stm32f103rb_bootloader.ld