inv_ui: Allow disabling numeric map item shortcuts

[Kamayana]

Summary

Interface "Allows disabling the numeric hotkeys for map items"

Purpose of change

Adds a new interface option for disabling numeric hotkeys in menus that interact with map items. These hotkeys take the numpad as input, and thus can easily lead to mistakes, as mentioned in #37980.

Describe the solution

Added a new setting, and then added an additional conditional to inventory_ui.cpp's inventory_selector::reassign_custom_invlets() that will cancel adding the shortcuts if that setting is false.

Describe alternatives you've considered

Adjusting inventory_ui to respect the key code setting, which would allow it to distinguish numpad keys from numeric keys. Alternately, allowing the alphabetical hotkeys to spill over to map items if there aren't enough items in the inventory to use up every letter. Both of these options seemed further beyond my scope and I wanted to keep it simple.

Testing

Started a new game as Evacuee, walked next to shelf with items, pressed 'w' to bring up wield menu. Numeric shortcuts are visible, and using the numpad wields an item. Went into options and turned "Use Numeric Item Shortcuts" to FALSE. Back in game, pressed 'w' to bring up wield menu. No numeric shortcuts are visible, and using the numpad navigates the menu. Turned the setting back to TRUE and the behavior went back to the default.

Additional context

[Kamayana]

Whoops, I'm a doofus. Pardon my git rust.