`GtkSourceCompletionContext` contains information about an attept to display completion proposals to the user based on typed text in the
[class@View].
When typing, [class@Completion] may use registered [iface@CompletionProvider] to determine if there may be results which could be
displayed. If so, a `GtkSourceCompletionContext` is created with information that is provided to the [iface@CompletionProvider] to
populate results which might be useful to the user.
[iface@CompletionProvider] are expected to provide [[email protected]] with [iface@CompletionProposal] which may be joined together in
a list of results for the user. They are also responsible for how the contents are displayed using [class@CompletionCell] which allows for
some level of customization.