Account for continuous panel when playing back in continuous view

[RMRattray]

Resolves: #16173
Resolves: #29928

Previously, when playing back music in continuous view mode, the sticky header, the ContinuousPanel, would cover up some of the music; the width of the header was rendered retrievable and the AbstractNotationPaintView::adjustCanvasPosition method modified to account for it, which prevents the playback cursor - or the selected element or range, or any other object of focus - from being covered by it.

• I signed the CLA
• The title of the PR describes the problem it addresses
• Each commit's message describes its purpose and effects, and references the issue it resolves
• If changes are extensive, there is a sequence of easily reviewable commits
• The code in the PR follows the coding rules
• There are no unnecessary changes
• The code compiles and runs on my machine, preferably after each commit individually
• I created a unit test or vtest to verify the changes I made (if applicable)

[cbjeukendrup]

Looks good to me, thanks!

[zacjansheski]

Looks like we lose the blue line in this PR once the page needs to scroll

video1262858885.mp4

[RMRattray]

Looks like we lose the blue line in this PR once the page needs to scroll

video1262858885.mp4

Ah! So it does - I should not have changed the second if-case; there is no reason to adjust by the left-side panel's width when matching on the right side, and doing so caused this strange dragging behavior. The PR has been modified not to do this.

It has also been brought to my attention that this commit addresses #29928 ; the message of the PR's one commit was modified to indicate this.

[cbjeukendrup]

@RMRattray I'm sorry but there's a merge conflict; I merged another PR and I thought it wouldn't interfere, but apparently it did. So you could please give this one a rebase? Thanks!

[RMRattray]

@RMRattray I'm sorry but there's a merge conflict; I merged another PR and I thought it wouldn't interfere, but apparently it did. So you could please give this one a rebase? Thanks!

Sure, no trouble!

[zacjansheski]

Tested on MacOS 15, Windows 11, Ubuntu 22.04.3. Approved
#16173 FIXED
#29928 FIXED

[cbjeukendrup]

Thanks @RMRattray! I believe this will make quite many people happy!