FilterNode allows forwarding selected methods to
its delegate, and filtering the others.
The filtering can be selected on a method basis
for most of important methods, but not for
get/setValue methods. The Node's value is used
throughout the IDE for some sideband communication
and when a Node is wrapped in FilterNode, this
sideband is broken.

I propose to allow forwarding these two methods as
well, by means of providing forwarding masks for
these two methods and by overriding the methods in
FilterNode to perform forwarding.

The API change consists solely of adding two
protected constants:
FilterNode.DELEGATE_SET_VALUE = 1 << 9;
FilterNode.DELEGATE_GET_VALUE = 1 << 10;

The constants will be stable and the behaviour of
the get/setValue will be driven by the value of
provided mask. The default mask will contain the
above flags set, which means change in behaviour
(after this change, the FilterNode will delegate
the get/setValue calls, which it didn't before).

The issue itself is tracked as issue #31006 and
blocks issue 9940