Readd searching for breeze decoration

Was missed in move from plasma-desktop.
We no longer write configs like
 library=org.kde.breeze
 theme=kwin4_decoration_qml_plastik
BUG:429298

CMakeLists.txt

@@ -90,6 +90,11 @@ set_package_properties(Phonon4Qt5 PROPERTIES
    DESCRIPTION "Qt-based audio library"
    TYPE REQUIRED)
 
+find_package(Breeze ${PROJECT_VERSION} CONFIG)
+set_package_properties(Breeze PROPERTIES
+                       TYPE OPTIONAL
+                       PURPOSE "For setting the default window decoration plugin")
+
 find_package(ZLIB)
 set_package_properties(ZLIB PROPERTIES DESCRIPTION "Support for gzip compressed files and data streams"
                        URL "https://www.zlib.net"

kcms/lookandfeel/CMakeLists.txt

@@ -4,6 +4,17 @@ add_definitions(-DTRANSLATION_DOMAIN=\"kcm_lookandfeel\")
 if(X11_Xcursor_FOUND)
     set(HAVE_XCURSOR TRUE)
 endif()
+
+if(${Breeze_FOUND})
+    if(${BREEZE_WITH_KDECORATION})
+        set(HAVE_BREEZE_DECO true)
+    else()
+        set(HAVE_BREEZE_DECO FALSE)
+    endif()
+else()
+    set(HAVE_BREEZE_DECO FALSE)
+endif()
+
 configure_file (config-kcm.h.cmake ${CMAKE_CURRENT_BINARY_DIR}/config-kcm.h )
 
 set(kcm_lookandfeel_SRCS

kcms/lookandfeel/config-kcm.h.cmake

@@ -1,3 +1,7 @@
 #cmakedefine HAVE_XFIXES 1
 #cmakedefine HAVE_XCURSOR 1
 #cmakedefine HAVE_BREEZE_DECO 1
+#ifdef HAVE_BREEZE_DECO
+#define BREEZE_KDECORATION_PLUGIN_ID "${BREEZE_KDECORATION_PLUGIN_ID}"
+#endif
+