Add joystick plugin (#39)

https://github.com/sony/flutter-elinux-plugins/issues/35

packages/joystick/elinux/CMakeLists.txt

@@ -0,0 +1,25 @@
+cmake_minimum_required(VERSION 3.10)
+set(PROJECT_NAME "joystick")
+project(${PROJECT_NAME} LANGUAGES CXX)
+
+# This value is used when generating builds using this plugin, so it must
+# not be changed
+set(PLUGIN_NAME "joystick_plugin")
+
+add_library(${PLUGIN_NAME} SHARED
+  "joystick_plugin.cc"
+  "linux_joystick.cc"
+)
+apply_standard_settings(${PLUGIN_NAME})
+set_target_properties(${PLUGIN_NAME} PROPERTIES
+  CXX_VISIBILITY_PRESET hidden)
+target_compile_definitions(${PLUGIN_NAME} PRIVATE FLUTTER_PLUGIN_IMPL)
+target_include_directories(${PLUGIN_NAME} INTERFACE
+  "${CMAKE_CURRENT_SOURCE_DIR}/include")
+target_link_libraries(${PLUGIN_NAME} PRIVATE flutter flutter_wrapper_plugin)
+
+# List of absolute paths to libraries that should be bundled with the plugin
+set(joystick_bundled_libraries
+  ""
+  PARENT_SCOPE
+)