ECMAddQtDesignerPlugin provides two macros that can be used to
replace the usage of the tool kgendesignerplugin from KDesignerPlugin.
This allows to have ECM-using libraries to create Qt Designer plugins without
the need for another separate tool.
For that purpose option structure & defaults are inspired from that one, to
allow simple porting. Main difference is that ECMAddQtDesignerPlugin
expects the widget metadata definition to be done in CMake code,
using a dedicated function, instead of in a ini-style separate ".widgets" file.
Porting of ".widgets" files basically means:
copy content into cmake, transform ini code into arguments to util method.
Key names need a bit of adaption, current names are open for dicussion.
Porting example:
```
[KActionSelector]
IncludeFile=kactionselector.h
ToolTip=A widget for selecting and arranging actions/objects
Group=Views (KF5)
```
gets
```
ecm_qtdesignerplugin_widget(KActionSelector
INCLUDE_FILE kactionselector.h
TOOLTIP "A widget for selecting and arranging actions/objects"
GROUP "Views (KF5)"
)
```