Provide Drag/Drop and Object Explorer Option in Query Tool Workspace

[anthonydb]

Describe the solution you'd like

Per #7708 (comment) ...

As a user, I would like to drag and drop table names, column names and other identifiers into a script in the Query Tool workspace. In the current implementation of workspaces, I cannot do this because the Object Explorer is only accessible in its own workspace.

Ideally, in the Query Tool workspace, I would like to have the Object Explorer as a collapsible pane.

Describe alternatives you've considered

1. I could use the "classic" interface. However, the new workspace layout has been set as the default option, and new users unfamiliar with pgAdmin wouldn't necessarily know they could switch.

2. I could use autocomplete by pressing CTRL + SPACE. However, doing so generates a list that begins with system items rather than table names in the database, as shown here:

Thus, unless I have some idea of the table name, the autocomplete is not helpful.