Fix regression causing flickery windows when hiding

[Jacalz]

Description:

This reverts commit 5bac179.

Reason for revert: This code runs when hiding and closing windows as well. Always doing a show results in flickering when trying to hide a second window by pressing a button inside that window. I don't know of a better solution so I just revert the PR for now to avoid the bug.

Checklist:

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

[coveralls]

coverage: 65.302% (-0.001%) from 65.303% when pulling 0e7c82c on Jacalz:fix-flickery-windows into 8be6541 on fyne-io:develop.

[andydotxyz]

It seems that the issue of flickering is Linux (or at least not Darwin) so perhaps this could be put inside a GOOS check instead of being reverted?

[Jacalz]

Would you mind just testing this with the following code first? It should allow you to replicate it easily.

package main

import (
	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("First")

	w2 := a.NewWindow("Second")
	w2.SetContent(widget.NewButton("Hide", w2.Hide))
	w2.Show()

	w.Resize(fyne.NewSquareSize(50))
	w.ShowAndRun()
}

[andydotxyz]

OMG yes that replicates on macOS too. With both windows visible.
Reverting fixes. That is the way - we need a different fix to this bug!