* PortalList: keep the tailing state across a reload
`auto_tail` turned `tail_range` back on for every apply, including a style reload
or an Android/iOS rotation, which pulled a list the user had scrolled up back to its end.
Now only a new list starts out following its end.
* CachedWidget: re-apply a cached widget that missed a reload
A cached widget that nothing held during a reload (e.g. one that only lives in an
AdaptiveView's inactive variant, or in a lazily built page) kept its old styling,
since adopting it from the cache never re-applied its template.
* `Cx::reload_generation` counts the whole-tree reload walks
* `CachedWidget` records the generation each widget was last applied at,
and requests a script reapply when it adopts one that's out of date
* CalloutTooltip: take its default colors from Splash
`CalloutTooltipOptions::default()` hardcoded the text and background colors in Rust,
and `draw_walk` always applied them, so apps couldn't theme their tooltips.
The options' colors are now `Option`s; `None` uses the tooltip's own `text_color`/`bg_color`,
which default to the same values as before.
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