`digitalWrite` has a wrong signature

Currently MegaAVR is one of the very few platforms where digitalWrite doesn't take a boolean for `digitalWrite` (there's no `digitalWrite(uint8_t pin, bool val)`), this causes unnecessary incompatibility with a massive selection of libraries out there.

The function's signature should either be changed or the core should overload the function.

Start by locating the core declaration and implementation of digitalWrite and compare its parameter types with the compatibility expected by Arduino libraries. The work is done when the MegaAVR core accepts a boolean value for digitalWrite(uint8_t pin, bool val), either through the signature or an overload, without breaking existing use.

Written by the indexing model from the issue text.