Add mechanisms to create a session from any registered runtime

[dhruvisompura]

We'll need to make the following changes to the services:

• Tweak runtimeSessionService to check all active sessions:
  - getConsoleSessionForRuntime: Return the active session for the provided runtime id, if one exists
  - getConsoleSessionForLanguage: Return the active session for the specified language id, if one exists
• positronConsoleService
• positronConsoleInstance

See docs for implementation details for panel views: https://code.visualstudio.com/docs/getstarted/getting-started#_access-the-terminal-from-the-panel-area

The UI will require the following new components:

• Add + button to console panel which creates a duplicate session of the current active runtime via runtimeSessionService.startNewRuntimeSession and makes the new runtime session the active runtime. When a new runtime session is created we should also have a new console instance for the session.
  • This button should be located in the console panel toolbar
• Add dropdown button next to + button which allows creating a session for any registered runtime from languageRuntimeService.registeredRuntimes.
  • This button will display the modal popup component containing a list of actions the user can take.

We'll want to restrict the number of sessions a user can create to 15 (an arbitrary number for now). We may want to make this a setting option that the user can change.

Testing

• Verify a session can be viewed/shutdown from the debugging runtime pane
• Verify a session can be shutdown via the console pane (the console UI tab should still stick around)
• When creating a new session, verify there is an output channel for the newly created session
• When creating a new session, verify the variables pane switches context to the new session. The variables pane should display variables for the new session only. The new session should be the active.
• Verify the number of sessions a user can create is limited to 15