Allow OpenWithMenuContribution to filter out currently active editor.

Allow OpenWithMenuContribution to filter out currently active editor.

Using o.s.ui.contribution.OpenWithMenuContribution:activeEditorId in
dynamic menuContrubution class reference activates active editor
filtering. Existing OpenWith menu contributions are not affected.

Several editor adapters now return null as editorId, thus they cannot be
filtered. This should dot be a problem, since the editors most likely do
not use OpenWith menu.

gitlab #624

Change-Id: I3adc13163ac74c5e1841842ef6b958084288202f