debugui: stop using `idFromPointer`

[hajimehoshi]

Now these controls use pointers as identifiers:

• TextField
• NumberField(F)
• Slider(F)
• Checkbox

The problem is, it is too easy to misuse this by passing a local variable's pointer.

In order to improve consistency with other controls like buttons, what about using pc (program counter) as identifiers?

This would require an additional string variable to distinguish controls in for loops, unfortunately.