Add STARTUP_SCRIPT option. M17 parity with M18. (#14953)

Marlin/Configuration_adv.h

Marlin/src/Marlin.cpp

Marlin/src/Marlin.h

Marlin/src/core/drivers.h

Marlin/src/feature/pause.cpp

Marlin/src/gcode/control/M17_M18_M84.cpp

Marlin/src/inc/Conditionals_post.h

Marlin/src/libs/L6470/L6470_Marlin.h

config/default/Configuration_adv.h

config/examples/3DFabXYZ/Migbot/Configuration_adv.h

config/examples/AlephObjects/TAZ4/Configuration_adv.h

config/examples/Alfawise/U20/Configuration_adv.h

config/examples/AliExpress/UM2pExt/Configuration_adv.h

config/examples/Anet/A2/Configuration_adv.h

config/examples/Anet/A2plus/Configuration_adv.h

config/examples/Anet/A6/Configuration_adv.h

config/examples/Anet/A8/Configuration_adv.h

config/examples/Anet/A8plus/Configuration_adv.h

config/examples/Anet/E16/Configuration_adv.h

config/examples/AnyCubic/i3/Configuration_adv.h