Handle Numpad Enter key as regular Enter key

[neolight1010]

This PR fixes #1959. The key-pressing checks of each editor mode were modified to treat the Numpad Enter key and the regular Enter key as equal. Specifically, the Numpad Enter key now works for the following:

• Code editor (newline, goto, find, etc.)
• Music editor.
• Regular menu.
• Surf menu.
• Going full screen with Alt+Enter.
• Runnning the current cart with Ctrl+Enter.

[joshgoebel]

Surely we can find a way to avoid repeating the enterWasPressed function over and over in every file?

[neolight1010]

Certainly @joshgoebel , thanks for the suggestion. I created the shared enterWasPressed function that uses the hold and period values used in studio.h, and the tic_core_enterp function that receives the hold and period values as arguments, similar to the interface of tic_api_keyp.