install session file for Plasma on Wayland session

This is known to work with at least sddm 0.13 and higher. It is listed
as "Plasma (wayland)".

REVIEW: 126098

CMakeLists.txt

@@ -105,6 +105,12 @@ install(FILES
         DESTINATION ${KDE_INSTALL_DATADIR}/xsessions
 )
 
+configure_file(plasmawayland.desktop.cmake ${CMAKE_CURRENT_BINARY_DIR}/plasmawayland.desktop)
+install(FILES
+        ${CMAKE_CURRENT_BINARY_DIR}/plasmawayland.desktop
+        DESTINATION ${KDE_INSTALL_DATADIR}/wayland-sessions
+)
+
 plasma_install_package(lookandfeel org.kde.breeze.desktop look-and-feel lookandfeel)
 
 if (INSTALL_SDDM_THEME)

plasmawayland.desktop.cmake

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Encoding=UTF-8
+Exec=${CMAKE_INSTALL_FULL_BINDIR}/startplasmacompositor
+TryExec=${CMAKE_INSTALL_FULL_BINDIR}/startplasmacompositor
+DesktopNames=KDE
+Name=Plasma
+Comment=Plasma by KDE
+X-KDE-PluginInfo-Version=${PROJECT_VERSION}