Fix timeline objects disappearing prematurely on wide-screens

[frenzibyte]

• Addresses alternative way to have notes disappear in editor timeline #18407

Turns out there's already logic for expanding the lifetime of hitobjects, and zooming in/out actually work fine. But when resizing the window to a wide aspect ratio, the issue becomes clear.

Resolved by computing the visible range more properly, by taking the ratio of the timeline's displayed portion and factor it into the track length to get the "visible time range".

Have added test coverage to ensure this works as expected.

[bdach]

I was very confused as to why this was apparently "more correct" than the old version. For all intents and purposes, DisplayableContent / Content.DrawWidth should be precisely equal to 1 / Zoom:

osu/osu.Game/Screens/Edit/Compose/Components/Timeline/ZoomableScrollContainer.cs

Line 131 in 83c2b27

private void updateZoomedContentWidth() => zoomedContent.Width = DrawWidth * currentZoom;

I believe that the reason why 1 / Zoom is not working correctly, is that the bug is actually in ZoomableScrollContainer - the container is not responding to draw size invalidations, and therefore changing the window size is potentially inadvertently changing the zoom level, therefore breaking the VisibleRange calculation too. Here's a video - captured on this branch - showing why I think this:

2022-05-29.17-47-53.mp4

Note how the zoom level snaps abruptly when I just nudge the buttons ever so slightly. The working theory is that when the window is being resized, the value of DisplayableContent changes, but Content.DrawWidth stays the same, which leads to Zoom having a stale/incorrect value.

[frenzibyte]

Ah, good find. Should probably have it fixed in this PR instead, will take a look whenever I get the chance.

[frenzibyte]

Have reverted the current change and fixed ZoomableScrollContainer to update its width on external size changes.

[smoogipoo]

Makes sense