Move border creation outside of layout pass

[jperedadnr]

Fixes #1538

This PR modifies the Borders#StrokeBorder class to avoid doing node creation on layout passes, by moving out the border creation to a method that is called only after the title label creation and when the width of the stackPane that wraps the user node changes.
The title label layout is overwritten only to relocate it properly.

This changes should increase notably the performance of any node wrapped with Borders.

Running the test attached to the issue shows now:

needs layout = false
needs layout = true
needs layout = false
needs layout = true

(that's it, no more infinite layout passes)

[abhinayagarwal]

I can reproduce this with the provided sample in issue #1538. I can further confirm that this PR fixes the issue. Overall, it looks like a good enhancement. Is there a particular reason why titleLabel is currently only relocated and not resized in layoutChildren ?

[jperedadnr]

I overwrote computePrefWidth for that, and that should do it.

Adding titleLabel.resize to the layout pass brings back the infinite layout passes.

For the test case for instance, the label width (without padding) is 26.5, while pref width value (without padding) is: 26.4609375.

Without this change, there is a constant fight between pref and width:

• StrokeBorders layoutChildren sets the label's width to its pref width, and Region::widthChanged calls requestParentLayout. During the layout, the width gets snapped (or set by computePrefWidth to a snapped value), and there is this log (adding a log to Region::widthChanged) repeated all over again (every pulse):

...
needs layout = false
value = 26.5 vs _width = 26.4609375
needs layout = true
value = 26.4609375 vs _width = 26.5
...

Of course, and option might be adding snap methods to the layout pass, but I guess computePrefWidth already takes care of that.