[3.x] Add built-in action toggle in Input Map settings

[timothyqiu]

Like in 4.0:

• Adds a "Show Built-in Actions" toggle.
• Display name error in the tooltip of the disabled Add button, so that controls won't exceed dialog boundary in some cases.

This is a reimplementation instead of a backport since the action map editor changed quite a lot in 4.0. But the new functions / variables still use the same name as their 4.0 counterpart.

[akien-mga]

Thanks!