🔨 Simplify generic variants, update DFU tool

[thinkyhead]

• Update to DFU tool 1.11.0 with minor patches — for better macOS compatibility (eventually). See this thread.
• Modify "variant" scripts to point the build.variants_dir at our folder (instead of copying into the platform).
• Rename some boards and variants to match siblings.

[thinkyhead]

Double-checked to make sure files are indeed being included, and it all seems good. Maple can't take the same approach, but maybe it's possible to set extra environment vars or other build flags to sort out #include <...> lines within the Maple variants.

[vehystrix]

Since the change in generic_create_variant.py I get build errors. I get as far as this:

Linking .pio\build\MKS_E3_V2\firmware.elf
arm-none-eabi-g++: error: C:/Users/VEH/Documents/3DPrint/Printer: No such file or directory
arm-none-eabi-g++: error: upgrades/Marlin/buildroot/share/PlatformIO/variants/MARLIN_MKS_E3/ldscript.ld: No such file or directory
*** [.pio\build\MKS_E3_V2\firmware.elf] Error 1

Note that I am using the path C:\Users\VEH\Documents\3DPrint\Printer upgrades\Marlin as my marlin source path. When I remove the space in the path, the build completes as it should.