[VSCode] Refactor Duo Quick Chat using a state machine POC

Problem to solve

Duo Quick Chat is getting complicated with multiple components relying on the side effects.

There are multiple listeners and we check different things across to determine whether we want to update the Quick Chat like gutter icon and keyboard bindings.

Proposal

Improved State Management: Refactor Duo Quick Chat to simplify the logics based on the suggestion from below.

Further details

Suggestion comment from @viktomas

• @viktomas started a discussion:

  (non-blocking) This is a more complex suggestion and it is related to this whole file, not just the feature in this MR. So it's not blocking.

  I think we got into a state where we should consider using a state machine here. Something like

  stateDiagram-v2
      [*] --> NoQuickChat: Initial State
      
      NoQuickChat --> QuickChatCurrentDoc: Open quick chat
      QuickChatCurrentDoc --> NoQuickChat: Close quick chat
      
      QuickChatCurrentDoc --> QuickChatDifferentDoc: Switch documents
      QuickChatDifferentDoc --> QuickChatCurrentDoc: Return to original document
      
      QuickChatCurrentDoc --> QuickChatCollapsed: Collapse chat
      QuickChatDifferentDoc --> QuickChatCollapsed: Collapse chat
      
      QuickChatCollapsed --> QuickChatCurrentDoc: Expand in current doc
      QuickChatCollapsed --> NoQuickChat: Close collapsed chat

  Then we would have a single "state changed event" and all the components like this context value, the gutter icon and so on could react to the state changes.

Links / references