Fix bubble animations overshooting in the timeline when SR/RRs are removed from an event

[ara4n]

Top-align message bubbles within their VStack of TimelineItemBubbledStylerView by adding a Spacer, so that the bubble doesn't drift around as the row shrinks when the TimelineItemStatusView empties due to the message no longer having SR/RRs. This causes the "bubble animation overshoots its target" bug in #4127. See the bug for videos of before & after.

The addition of the Spacer empirically adds a gap between the bubbles, which we compensate for with some negative spacing on the VStack.

Empirically this seems to work okay, although I did see some intermittent weirdness with the row at the top of the UITableView vanishing as the new row gets added at the bottom - feeling a bit like a cell reuse bug of some kind. However, this seems very intermittent, and less distracting than the previous mangled animation (given you're not looking at the top of the screen when you hit send on a message).

Edit: The fixes elsewhere seem to have made this behaviour worse - the row at the top of the table blinks off & on distractingly as rows are added to the bottom. It definitely looks like a cell reuse bug of some kind, or maybe UITableView still getting very confused when the heights of its rows change. Unfortunately this looks bad enough to merit marking this PR as a draft until it can be investigated further.

(Edit: there's another problem caused by the SR-hiding animation racing with UITableView's new-row animation and thoroughly confusing UITableView, as per #4127 (comment) - will add a fix here once confident in it.) Edit: now fixed in 9df170e

Pull Request Checklist

• I read the contributing guide.
• Pull request contains a changelog label.

UI changes have been tested with:

• iPhone and iPad simulators in portrait and landscape orientations.
• Dark mode enabled and disabled.
• Various sizes of dynamic type.
• Voiceover enabled.

[github-actions]

	Warnings
⚠️	You seem to have made changes to views. Please consider adding screenshots.

Generated by 🚫 Danger Swift against ecc9953

[codecov]

❌ 14 Tests Failed:

Tests completed	Failed	Passed	Skipped
1007	14	993	0

View the top 3 failed test(s) by shortest run time

PreviewTests::testRedactedRoomTimelineView()

Stack Traces | 0.643s run time

failed - Snapshot "iPhone 16-en-GB-0" does not match reference.

@−
"file:.../__Snapshots__/PreviewTests/redactedRoomTimelineView.iPhone-16-en-GB-0.png"
@+
"file:.../tmp/PreviewTests/redactedRoomTimelineView.iPhone-16-en-GB-0.png"

To configure output for a custom diff tool, use 'withSnapshotTesting'. For example:

    withSnapshotTesting(diffTool: .ksdiff) {
      // ...
    }

The percentage of pixels that match 0.947876 is less than required 1.0
The lowest perceptual color precision 0.28812498 is less than required 0.98 (PreviewTests/Sources/PreviewTests.swift:106)

PreviewTests::testEmoteRoomTimelineView()

Stack Traces | 0.735s run time

failed - Snapshot "iPhone 16-en-GB-0" does not match reference.

@−
"file:.../__Snapshots__/PreviewTests/emoteRoomTimelineView.iPhone-16-en-GB-0.png"
@+
"file:.../tmp/PreviewTests/emoteRoomTimelineView.iPhone-16-en-GB-0.png"

To configure output for a custom diff tool, use 'withSnapshotTesting'. For example:

    withSnapshotTesting(diffTool: .ksdiff) {
      // ...
    }

The percentage of pixels that match 0.6843262 is less than required 1.0
The lowest perceptual color precision 0.18624997 is less than required 0.98 (PreviewTests/Sources/PreviewTests.swift:106)

PreviewTests::testNoticeRoomTimelineView()

Stack Traces | 0.781s run time

failed - Snapshot "iPhone 16-en-GB-0" does not match reference.

@−
"file:.../__Snapshots__/PreviewTests/noticeRoomTimelineView.iPhone-16-en-GB-0.png"
@+
"file:.../tmp/PreviewTests/noticeRoomTimelineView.iPhone-16-en-GB-0.png"

To configure output for a custom diff tool, use 'withSnapshotTesting'. For example:

    withSnapshotTesting(diffTool: .ksdiff) {
      // ...
    }

The percentage of pixels that match 0.68725586 is less than required 1.0
The lowest perceptual color precision 0.18624997 is less than required 0.98 (PreviewTests/Sources/PreviewTests.swift:106)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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