This pull request implements the new
`ITerminalConnection::ConnectionState` interface (enum, event) and
connects it through TerminalControl to Pane, Tab and App as specified in
#2039. It does so to implement `closeOnExit` = `graceful` in addition to
the other two normal CoE types.
It also:
* exposes the singleton `CascadiaSettings` through a function that
looks it up by using the current Xaml application's `AppLogic`.
* In so doing, we've broken up the weird runaround where App tells
TerminalSettings to CloseOnExit and then later another part of App
_asks TerminalControl_ to tell it what TerminalSettings said App
told it earlier. `:crazy_eyes:`
* wires up a bunch of connection state points to `AzureConnection`.
This required moving the Azure connection's state machine to use another
enum name (oops).
* ships a helper class for managing connection state transitions.
* contains a bunch of template magic.
* introduces `WINRT_CALLBACK`, a oneshot callback like `TYPED_EVENT`.
* replaces a bunch of disparate `_connecting` and `_closing` members
with just one uberstate.
* updates the JSON schema and defaults to prefer closeOnExit: graceful
* updates all relevant documentation
Specified in #2039Fixes#2563
Co-authored-by: mcpiroman <38111589+mcpiroman@users.noreply.github.com>
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