UI: Refactor / Clean up addNudge

[gxalpha]

Description

Refactors how nudges are registered by using a lambda instead of separate slot functions. Significantly cuts down on code.

Motivation and Context

About a year ago when reviewing #6326 Jim mentioned that this should probably get cleaned up. I stumbled across this code again and remembered that.

How Has This Been Tested?

macOS 13.2 Tested nudging in all directions, both with and without shift.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.