Fix ScrollToBottom and ScrollToTop

[lorypelli]

Description:

I managed to fix scroll to bottom issue, I tested and it works...

Fixes #2917

Checklist:

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

Where applicable:

• Public APIs match existing style and have Since: line.
• Any breaking changes have a deprecation path or have been discussed.
• Check for binary size increases when importing new modules.

[andydotxyz]

I have realised that the tests are basically no-ops as the X/Y and assertions were confused.

Try the following test cases (maybe commit them in this PR if you agree with them):

func TestScrollContainer_ScrollToTop(t *testing.T) {
	rect := canvas.NewRectangle(color.Black)
	rect.SetMinSize(fyne.NewSize(100, 500))
	scroll := NewScroll(rect)
	scroll.Resize(fyne.NewSize(100, 50))

	scroll.scrollBy(0, -100)
	assert.Equal(t, float32(100), scroll.Offset.Y)

	scroll.ScrollToTop()
	assert.Equal(t, float32(0), scroll.Offset.Y)
}

func TestScrollContainer_ScrollToBottom(t *testing.T) {
	rect := canvas.NewRectangle(color.Black)
	rect.SetMinSize(fyne.NewSize(100, 500))
	scroll := NewScroll(rect)
	scroll.Resize(fyne.NewSize(100, 50))
	scroll.ScrollToBottom()
	assert.Equal(t, float32(450), scroll.Offset.Y)
}

[andydotxyz]

Great work but the ScrollToBottom does not seem correct - it's got two codepaths and can be simplified as noted inline.

[andydotxyz]

Good catch!

[andydotxyz]

This fix doesn't seem right - making a change then refreshing but then also making another change.

Really it should call scrollBy so the fix should be revising the parameters to that method.
And that Refresh looks like it's not needed any more.

[Jacalz]

You should also save the result of MinSize() and Size() instead of computing it multiple times in succession.