Fix NavigationToolbar2QT height

[timhoffm]

PR Summary

Fixes #10891. See also #14518.

Before:

After:

Note

This and #14518 only change the behavior for non-HiDPI screens.
I'm wondering if the distinction is still necessary. I would assume that Qt should handle this out of the box without manual tuning.

[anntzer]

I don't have a real high-dpi display available but you can fake one by setting QT_SCALE_FACTOR (e.g. to 2); based on that I think we could perhaps even just delete both

        # Esthetic adjustments - we need to set these explicitly in PyQt5
        # otherwise the layout looks different - but we don't want to set it if
        # not using HiDPI icons otherwise they look worse than before.
        if is_pyqt5() and self.canvas._dpi_ratio > 1:
            self.setIconSize(QtCore.QSize(24, 24))
            self.layout().setSpacing(12)

(in _init_toolbar) and the whole sizeHint (just relying on the base class implementation), instead of doing any special handling for high dpi...

[anntzer]

approving as clearly an improvement, but perhaps we can do even better per the comment above?

[tacaswell]

Merging this as it makes things better and defer a bigger overhaul to a follow on.

To be consistent with #14518 this should be backported, where as I would prefer to not backport a PR with @anntzer 's suggestions.

[anntzer]

No worries, I made #14702 :)

[QuLogic]

@meeseeksdev backport to v3.1.x