Decoration tooltip is not refreshed or purge when the diagram is refreshed

[peransin-obeo]

When the tooltip of a decoration is evaluated on MouseHover event, the result is stored in the cache of the figure.

See

sirius-desktop/plugins/org.eclipse.sirius.diagram.ui/src-diag/org/eclipse/sirius/diagram/ui/tools/internal/decoration/SiriusGenericDecorator.java

Line 695 in 275f886

toolTip = getDecorationTooltip(decoDescriptor);

When the diagram is refreshed on a semantic change, this cache is not purged.
The tooltip will display an old value until the diagram is closed or the view impacted by a change.

Tested on Sirius 7.1.0.