Add characters_ignoring_modifiers to get chars ignoring modifiers on keyup/down events

[eugenesvk]

Copy&pasted the existing pub fn characters(&self) with a different constant

https://developer.apple.com/documentation/appkit/nsevent/1524605-charactersignoringmodifiers

(btw, is

• characters_ignoring_modifiers verbose really better to read vs
• chars_no_mods (the verbosity level of constraint_greater_than_or_equal_to makes it worse imo)

[eugenesvk]

rebased

The formatting checks/tests seem to run and fail on all the code in the repo, not specific to this, so not sure what to fix here