PR summary

With X11, there is only ever a single scale, regardless of monitors as in Wayland, so it's always the highest scale (i.e., it's 2 if you have 1.5&1-scaled monitors). Thus we get no change events and don't update the internal scale. On Wayland though, as noted in the other issue from Qt devs, you only get the fractional scale after the first expose, so there's always at least one event there.

In the older/pre-#30345 code path, inshowEvent, we'd call_update_screen to set callbacks for its changes, and thatalso called_update_pixel_ratio. In the new code, we don't have that initial call, and because Wayland always has at least one event at startup, it all seemed to work.

So just add the_update_pixel_ratio call in the new code path as well. On X11, this will be the highest integer scale needed and never changes. On Wayland, this will also be the rounded-up integer scale, but if using fractional scaling, will change with a subsequent event to the correct one. This does cause a few extra changes on startup, but should be more consistent across platforms.

Fixes#30386

PR checklist

• "closes #0000" is in the body of the PR description tolink the related issue
• new and changed code istested
• [n/a]Plotting related features are demonstrated in anexample
• [n/a]New Features andAPI Changes are noted with adirective and release note
• [n/a] Documentation complies withgeneral anddocstring guidelines