Document Editor: add "Go to Document..." menu item

[awqk]

Main/Document menu: Select from sorted list of documents, filter list by starting to type document name.

Project Tree View context menu: Filter the list to show only sub-items of the selected item.

The document list could be a list of all documents in a project, or the list of recently opened documents (once document history is available, see #1440). Example implementation: VSCode/"Go To File..."

Selecting a document opens the document in the Editor.

[awqk]

Option: add two menu items, one opening the document in the Editor, the other opening it in the Viewer

• re-label existing menu-items "Open Document" to "Open Selected Document"
• add menu-item "Open Document..."
• re-label existing menu-items "View Document" to "View Selected Document"
• add menu-item "View Document..."