Create an `ipl\Compat\Form` version of `ConfigForm`

[TheSyscall]

Is your feature request related to a problem? Please describe.

Modules commonly have INI-based configuration files.
We have ConfigForm to easily create edit these configuration files.
ConfigForm is sadly based on the old Zend_Forms.

Describe the solution you'd like

A modern ipl\Compat\Form based version would allow module developers to not have to reimplement this functionality.

Describe alternatives you've considered

• Have people duplicate functionality
• Use ConfigForm forever

Additional context

• We should also port showConfiguration.phtml to a Widget.
• A tiny improvement to the field naming would be to use "__" as the delimiter between the INI-section and key name would allow for section names containing "_".