Add ECMAddQtDesignerPlugin

Summary:
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)"
)
```

Reviewers: #build_system, #frameworks

Subscribers: apol, kde-frameworks-devel, kde-buildsystem

Tags: #frameworks, #build_system

Differential Revision: https://phabricator.kde.org/D22724

1 files changed, 1 insertions, 0 deletions

diff --git a/docs/module/ECMAddQtDesignerPlugin.rst b/docs/module/ECMAddQtDesignerPlugin.rst
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+.. ecm-module:: ../../modules/ECMAddQtDesignerPlugin.cmake