Code pane context menu

[retailcoder]

We need to implement the code pane context menu completely from scratch, including the bare-bones stuff like Copy and Paste (surely we want these commands in the Rubberduck Editor 🤔😂).

TODO list a subtask for each command to wire up here

Note: some of these commands would remain no-op (and hidden) until a corresponding LSP server method is actually implemented, i.e. we want to wire up "find references" even if the RPC request for it comes back in error.

[mansellan]

Would be good to make some of the context menus more... contextual too, for example how VS solution explorer changes radically depending on tree node type.

[retailcoder]

Explorer contexts:

• Project context, for the project nodes
• Library context, for the project/library reference nodes
• Folder context, for folder nodes

Shared contexts:

• Module context, for module nodes and when the selection/caret isn't anywhere special
• Member context, for member nodes and when the selection/caret is on or inside a member (including module-level members; not necessarily a procedure)

Additional editor contexts:

• Local context, when the selection/caret is on a local variable or parameter declaration or reference.
• Expression context, when the selection/caret is in an expression.
• Literal context, when the selection/caret is on a literal token of any kind, including strings.
• Comment context, when we're in a comment.
• Annotation context, when the comment is actually an annotation.
• Marker context when the comment is (or contains) a recognized TODO marker.

Any others?

Identifying the context could greatly simplify the commands' CanExecute conditions and avoid repeated/redundant checks if done right. A mechanism to discover the current context should be put in place first (some LSP server requests will be needed for that).