[EW] Moving sections or blocks from outline panel detaches comments

#1073 added a comments feature. While working on #1279, discovered that moving a section from the outline panel detaches comments because it rebuilds the entire doc rather than moving anything, so every comment anchor in the drag range breaks. Same case with moving a block, where it splices instead of rebuilding, but still deletes and then then inserts which breaks Yjs relative positioning.

Should be picked up once #1315 is in, which refactors the move logic to `splitSections`/`rebuildSections`.