ivi-homescreen: improve AGL integration

ivi-homescreen: improve AGL integration

Changes:
- For now add local patches for three changes that Marius has
  submitted upstream that fix issues with respect to running as
  a normal application against agl-compositor and configuration
  via the JSON configuration file.  The first of these patches has
  been merged upstream, but bumping the level of meta-flutter to
  get it brings other rework that it seems perhaps better to wait
  on a tagged upstream release for.
- Add another patch to add a '--app-id' command-line option to
  the embedder.  This avoids needing to use a JSON configuration
  file for simple (i.e. non-homescreen) applications when running
  multiple apps against agl-compositor.  The use of the example JSON
  file for the ivi-homescreen recipe itself has been left alone for
  now since it provides a reference for doing so.
- Rename the embedder binary from "homescreen" to "flutter" to
  avoid collision with the existing Qt homescreen application in
  meta-agl-demo.  This allows integrating Flutter applications into
  images using the Qt homescreen for testing in the period while a
  Flutter replacement is worked on.  Discussion about possibly
  renaming the embedder to something more generic along these lines
  has started with upstream.
- Split the embedder binary into a separate package from the
  ivi-homescreen package that contains the systemd unit file.
  We do not want the "homescreen" systemd unit when using the
  embedder in other images that use applaunchd, so this split seems
  the most straightforward way to avoid pulling it in.
- Remove installing the "homescreen" system level systemd unit, as
  it does not get used in agl-image-flutter (it is installed as a
  user unit instead).

Bug-AGL: SPEC-4485

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I9f02f4312cf8c77ab224a3de8114c7fc3f4f6d36