Expose more env builds in PlatformIO extension

Marlin/src/pins/pins.h

 #elif MB(MKS_ROBIN_PRO_V2)
   #include "stm32f4/pins_MKS_ROBIN_PRO_V2.h"    // STM32F4                                env:mks_robin_pro2
 #elif MB(MKS_ROBIN_NANO_V3)
-  #include "stm32f4/pins_MKS_ROBIN_NANO_V3.h"   // STM32F4                                env:mks_robin_nano_v3 env:mks_robin_nano_v3_usb_flash_drive
+  #include "stm32f4/pins_MKS_ROBIN_NANO_V3.h"   // STM32F4                                env:mks_robin_nano_v3 env:mks_robin_nano_v3_usb_flash_drive env:mks_robin_nano_v3_usb_flash_drive_msc
 #elif MB(ANET_ET4)
   #include "stm32f4/pins_ANET_ET4.h"            // STM32F4                                env:Anet_ET4_OpenBLT
 #elif MB(ANET_ET4P)

platformio.ini

 # Lerdge X
 #
 [env:LERDGEX]
+platform             = ${lerdge_common.platform}
 extends              = lerdge_common
 board_build.firmware = Lerdge_X_firmware_force.bin
 
 # Lerdge X with USB Flash Drive Support
 #
 [env:LERDGEX_usb_flash_drive]
+platform          = ${LERDGEX.platform}
 extends           = LERDGEX
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 # Lerdge S
 #
 [env:LERDGES]
+platform             = ${lerdge_common.platform}
 extends              = lerdge_common
 board_build.firmware = Lerdge_firmware_force.bin
 
 # Lerdge S with USB Flash Drive Support
 #
 [env:LERDGES_usb_flash_drive]
+platform          = ${LERDGES.platform}
 extends           = LERDGES
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
 # Lerdge K
 #
 [env:LERDGEK]
+platform             = ${lerdge_common.platform}
 extends              = lerdge_common
 board_build.firmware = Lerdge_K_firmware_force.bin
 build_flags          = ${lerdge_common.build_flags}
 # Lerdge K with USB Flash Drive Support
 #
 [env:LERDGEK_usb_flash_drive]
+platform          = ${LERDGEK.platform}
 extends           = LERDGEK
 platform_packages = ${stm32_flash_drive.platform_packages}
 build_flags       = ${stm32_flash_drive.build_flags}
   buildroot/share/PlatformIO/scripts/stm32_bootloader.py
 
 #
+# This SPI is used by Robin Nano V3
+#
+[stm32f4_I2C1]
+build_flags = -DPIN_WIRE_SCL=PB6 -DPIN_WIRE_SDA=PB7
+
+#
 # MKS Robin Nano V3
 #
 [env:mks_robin_nano_v3]
 platform             = ${common_stm32.platform}
 extends              = common_stm32
-build_flags          = ${common_stm32.build_flags} -DHAL_PCD_MODULE_ENABLED -DUSBCON -DUSBD_USE_CDC -DPIN_WIRE_SCL=PB6 -DPIN_WIRE_SDA=PB7
+build_flags          = ${common_stm32.build_flags} ${stm32f4_I2C1.build_flags} -DHAL_PCD_MODULE_ENABLED -DUSBCON -DUSBD_USE_CDC
 board                = genericSTM32F407VGT6
 board_build.core     = stm32
 board_build.variant  = MARLIN_F4x7Vx
 [env:mks_robin_nano_v3_usb_flash_drive]
 extends           = env:mks_robin_nano_v3
 platform_packages = ${stm32_flash_drive.platform_packages}
-build_flags       = ${stm32_flash_drive.build_flags}
-  -DPIN_WIRE_SCL=PB6 -DPIN_WIRE_SDA=PB7
+build_flags       = ${stm32_flash_drive.build_flags} ${stm32f4_I2C1.build_flags}
   -DUSBCON
   -DUSE_USBHOST_HS
   -DUSBD_IRQ_PRIO=5
 # Currently, using a STM32duino fork, until USB Host and USB Device MSC get merged
 #
 [env:mks_robin_nano_v3_usb_flash_drive_msc]
+platform          = ${common_stm32.platform}
 extends           = env:mks_robin_nano_v3
 platform_packages = framework-arduinoststm32@https://github.com/rhapsodyv/Arduino_Core_STM32/archive/usb-host-msc-cdc-msc.zip
 build_unflags     = ${common_stm32.build_unflags} -DUSBD_USE_CDC
-build_flags       = ${stm32_flash_drive.build_flags}
-  -DPIN_WIRE_SCL=PB6 -DPIN_WIRE_SDA=PB7
+build_flags       = ${stm32_flash_drive.build_flags} ${stm32f4_I2C1.build_flags}
   -DUSBCON
   -DUSE_USBHOST_HS
   -DUSBD_IRQ_PRIO=5