[429682] Remove ModelingProject.MODELING_PROJECT_PREDICATE

Removed because it exposed a Guava-specific type in our API. Can be
replaced by calls to ModelingProject.hasModelingProjectNature() instead.

Bug: 429682
Change-Id: I0c514228348f62a7f09f6a23b2f2172fd296ea8c
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[429682] Remove Options.isSome() predicate

It was a simple wrapper around Option.some() and exposed a
Guava-specific type for no good reason. Also, it was not used anywhere
in Sirius itself.

Bug: 429682
Change-Id: I8c4cc2d22552cbb8bab5661f5a5bedbcbddf1eeb
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[429682] Remove inheritance from Relation to Function

This keeps the same API but avoids a reference to a Guava-specific API.

Bug: 429682
Change-Id: I86954fe7efaccc5222f7ce8a7f1d5832c128308a
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>