For node and cpp, I use relative links to point to the slint language
reference documentation.
For the slint crate documentation I create a link to
https://slint-ui.com/releases/VERSION/... instead: This needs to work from
docs.rs as well as from our own docs area on slint-ui.com! That is
pretty ugly: I can not even define constants for this as the crate docs
need to come before anything else.
This is listed under the reference ("how to") and explains `SIXTYFPS_SLOW_ANIMATIONS`, SIXTYFPS_DEBUG_PERFORMANCE` as well as `SIXTYFPS_SCALE_FACTOR`.
cc #728