Even though the ST terminator is the only officially supported
terminator, some applications still rely on BEL to work properly. Both
have been supported historically, however there was no way for the
terminal to tell which terminator was used.
Since OSC escapes frequently offer the `?` parameter to query for the
current format, some applications expect the response terminator to
match the request terminator. To make it possible to support this, the
osc_dispatcher is now informed when the BEL terminator was used.
Since the C1 ST terminator was not yet supported for OSC escapes,
support for it has also been added.