Add transition/t8n keyword to do/redo macros

[Lavorther]

Is your feature request related to a problem?
I've seen a few questions on the Twine Discord server asking how to add transitions to the <<do>> or <<redo>> macros, which currently always update instantly.

Describe the solution you'd like.
Unlike the various link macros such as <<linkreplace>>, and other DOM macros like <<append>> and <<replace>>, neither <<do>> nor <<redo>> accepts transition or the shortened t8n keyword to trigger a fade-in effect when the contents are updated. Adding support for these keywords to one or both macros will allow users to easily create fade-in effects on the updated elements affected by the do/redo macros.

Describe alternatives you've considered.
While it is fairly trivial to manually add fade-in effects through CSS to affected elements, this might still be beyond the CSS knowledge of the average user. Having a transition keyword built into the macros itself is much easier, and more in line with other DOM macros SugarCube offers.

Additional context.
None.