Update meta-flutter

Update meta-flutter

- meta-flutter updates
  Deprecate FLUTTER_CHANNEL in favor of FLUTTER_SDK_TAG
  Remove need for TARGET_GCC_VERSION and FLUTTER_CLANG_VERSION variables
  Enable building for private engine branches
  vk-flutter-engine recipes (temporary till Vulkan PR is merged to master)
  ivi-homescreen package parameters for setting EGL GLES 2/3, EGL Context version, EGL Transparency flag.
  separate package for flutter engine_sdk.  Allows optional install to target image
  default FLUTTER_CHANNEL = "stable", opposed to "beta".
  FLUTTER_APPLICATION_PATH variable to support monolithic flutter app repos.  Allows setting project path from base repo.
  FLUTTER_EXTRA_BUILD_ARGS to pass parameters to 'flutter build bundle'.
  Add build dependency libxbcommon required for text plugin support

Signed-off-by: Joel Winarske <joel.winarske@gmail.com>
Change-Id: Ie362b6b9669940500d930543cf5262b8f9d15c09