all: refactor windows code out of core

There are still some links from core to window but its now separate
enough to fix PanelWindow in qml tooling.

src/window/CMakeLists.txt

@@ -0,0 +1,23 @@
+qt_add_library(quickshell-window STATIC
+	proxywindow.cpp
+	windowinterface.cpp
+	panelinterface.cpp
+	floatingwindow.cpp
+	popupwindow.cpp
+)
+
+qt_add_qml_module(quickshell-window
+	URI Quickshell._Window
+	VERSION 0.1
+)
+
+target_link_libraries(quickshell-window PRIVATE ${QT_DEPS} Qt6::QuickPrivate)
+
+qs_pch(quickshell-window)
+qs_pch(quickshell-windowplugin)
+
+target_link_libraries(quickshell PRIVATE quickshell-windowplugin)
+
+if (BUILD_TESTING)
+	add_subdirectory(test)
+endif()