Re-enabled CTRL+SHIFT+R resource search dialog in org.simantics.debug.ui

Re-enabled CTRL+SHIFT+R resource search dialog in org.simantics.debug.ui

This fixes the old problem where the index searches were not limited to
e.g. a 1000 hits but to Integer.MAX_VALUE instead. If the user happened
to write 'a' into the search field, this would return pretty much every
indexed resource and kill the JVM eventually.

This also fixes a problem from
org.simantics.modeling.ui.diagramEditor.DiagramViewer which did not
check diagram resource immutability before attempting to write a diagram
page description to it because it was missing. This can happen if you
use the resource search dialog to open e.g. diagram symbols from the
ontologies.

refs #6855

Change-Id: Id341871847e0ea8bdbc036e8023821ab0556a3cb