Minor refactor of refresh code in base widgets

[Jacalz]

Description:

Removing some code duplication for how methods were refreshing the widget. I also reordered unexported methods to be in the correct order. This does move .Hide() and .Show() away from doing a canvas.Refresh() which I think is both more correct and a performance win, right?

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

coverage: 59.353% (+0.04%) from 59.316%
when pulling 7114445 on Jacalz:minor-base-widget-cleanup
into e6225b5 on fyne-io:develop.

[andydotxyz]

This confuses Widget.Refresh() and canvas.Refresh(Widget).
This means that when hiding a BaseWidget it will now refresh the tree of widgets which it did not do before, as it just told the driver that those items should be removed from cache.

[Jacalz]

So it should only refresh on show if I understand you correctly? Or not refresh at all for show/hide?

[Jacalz]

I'm really confused about the difference between canvas.Refresh() for a widget and refresh on that widget directly.

[andydotxyz]

Calling Widget.Refresh cascades into the widget renderer and probably all of its children to redraw each canvas object.
canvas.Refresh(obj) just tells the driver that the item should be purged from the cache - so if it is then hidden no further code will be executed until it is shown again.

[Jacalz]

Ah, alright. I'll close this and do the refactoring in some future work after #5388 has been merged