This can happen if the same project has two or more Q_IMPORT_PLUGIN
macros in their source. And that can happen when converting from qmake-
based builds to CMake, as qmake didn't generate a source file with the
macro but CMake does.
[ChangeLog][QtCore][QPluginLoader] staticInstances() will not call
duplicated registrations of the same instantiation function, which can
only happen as a result of duplicated Q_IMPORT_PLUGIN for the same
plugin name.
Fixes: QTBUG-102745
Pick-to: 6.2 6.5
Change-Id: Idd5e1bb52be047d7b4fffffd174fb9dd62d8583d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
2f226336a2