U (and P, S, R, T, A, E, M, F, L) kept one reveal filter for the whole
Timeline and replaced the set of open layers with the selected ones, so
revealing on one layer closed every other layer and dropped their
reveals.
Each layer now has its own filter (TimelineState::layer_reveal; an open
layer without one shows its whole tree). A shortcut applies to the
selected layers (all layers with none selected) through apply_reveal and
leaves the others as they are; `reveal` stays the last shortcut's filter
for toggling and Shift-adding. U's results replace only the target
layers' earlier picks, so U after UU shows the keyframed properties
again. anim.reveal tells the Timeline which layers it looked at, so a
layer with nothing keyframed closes. Twirling a layer by hand, Ctrl+`
and Collapse All clear the filters they cover.
Test: reveal_shortcuts_leave_unselected_layers_alone.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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