Add a core option to control the Diagnostic input

[AkimanBengus]

This new core option allows the user to choose between different input or combo of inputs to activate the Diagnostic.

• Hold Start
• Start + A + B
• Hold Start + A + B
• Start + L + R
• Hold Start + L + R
• Hold Select
• Select + A + B
• Hold Select + A + B
• Select + L + R
• Hold Select + L + R

By default the option is set on None.