[435087] Reduce Sirius decoratorProviders extensions contexts to Sirius
elements

Providers will not be initialized while no Sirius diagram is open.

Bug: 435087
Change-Id: I9f05f2e371640a1110d4de38c28d4e873bdc98aa
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
[435182] Enable border nodes resize when the parent is a list

Bug: 435182
Change-Id: If2c5b6e45c1507cec15d7e4a88b5301c94b1747c
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
[435087] Additional extensions to GMF services contexts restrictions

Do not instantiate our edit policy providers and modeling assistant
provider while no Sirius diagram is open.

Restrict the scope of the ChangeBoundRequestRecorderEditPolicyProvider
to ISiriusEditPart (all edit parts in Sirius inherits from this marker,
if clients extend one of the Sirius edit part, they will provide an
ISiriusEditPart).

Bug: 435087
Change-Id: I8fc5dc858978a7b97fc1e88c3f94e08b38231ac8
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>
[cleanup] Avoid NPE during platform shutdown

Change-Id: Idee97760ce975d69b4362f70a2263cb1b7bb7b07
Signed-off-by: Maxime PORHEL <maxime.porhel@obeo.fr>