Extract DriveDelegate interface

[seanpdoyle]

The FrameController depends on the application's singleton Session
instance in several ways:

• it drives the History
• it determines whether or not an Element is "enabled" to navigate a
  page or frame
• it preloads links
• it dispatches turbo:frame-render and turbo:frame-load events
• it can initiate a Visit

This commit codifies those dependent behaviors by creating the
DriveDelegate interface and declaring the Session class as an
extension of that interface.

With the codification of the DriveDelegate responsibilities
established, managing turbo:frame-render and turbo:frame-load events
feels out of scope. To resolve that, this commit migrates the
Session.frameRendered and Session.frameLoaded methods to the
FrameController, and omits them from the DriveDelegate interface.

The FrameController still directly imports the singleton instance of
the Session from the src/core/index module, but assigns it to a
delegate: DriveDelegate property for use throughout the class.

The next step would be to find a way to forward the session instance
into the FrameElement.delegateConstructor assignment.

[marcoroth]

I really appreciate the work being done here, this is a really good extraction and refactoring!

I just have one question: what was your thought around having frameMissingFromResponse() as part of the DriveDelegate interface?

Why would other potential classes (that have a DriveDelegate) care about dispatching a warning about missing frames? Isn't that the sole responsibility of the FrameController?

[seanpdoyle]

@marcoroth these changes were proposed in the early stages of missing frame handling. I've rebased and moved all frame-related checks to the FrameController.

[marcoroth]

Ah, that would explain it!

This looks good from my side! 🥳

[seanpdoyle]

@manuelpuyol @kevinmcconnell I'd really appreciate a review of this changeset, if you're able to provide some.