Install QtPlugins.cmake.in

Added rule to install missing QtPlugins.cmake.in.

Change-Id: I485dadd56ee2dd435406d97399b32dc6390cebff
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtBaseGlobalTargets.cmake

@@ -183,6 +183,7 @@ qt_copy_or_install(FILES
                    cmake/QtModuleDependencies.cmake.in
                    cmake/QtModuleToolsDependencies.cmake.in
                    cmake/QtModuleToolsConfig.cmake.in
+                   cmake/QtPlugins.cmake.in
                    cmake/QtPluginConfig.cmake.in
                    cmake/QtPluginDependencies.cmake.in
     DESTINATION "${__GlobalConfig_install_dir}"