[475176] Remove the dependency to Acceleo MTL from Sirius Interpreter

* The ContentProposalWithReplacement can now provide an image for the
  proposal. Other interpreters will be able to provide images too in the
  future.
* A ContentProposalBuilder has been introduced to create content
  proposals more easily.
* The MTL and AQL interperters are now using the content proposal
  builder which allow us to remove the hardcoded dependency from
  org.eclipse.sirius.interpreter to the Acceleo MTL interpreter.
* The Target Platforms have been modified to consume Acceleo nightly,
  which is needed to leverage new completion-related APIs.

Bug: 475176
Change-Id: I3fa4b0a65e8aa23e35411c94e942433a7ffd4a86
Signed-off-by: Stéphane Bégaudeau <stephane.begaudeau@obeo.fr>
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
25 files changed