New NUI widgets (`EmptyIfInvisibleContainer`, `UIBackingBox` and `UILabelledIcon`)

[BenjaminAmos]

Description

This pull request adds some now NUI widgets that will be used in when porting the remaining built-in UI screens to use NUI. It also makes some minor changes to the default UILoadBar style, which was unnecesarily constraining the size of load bars.

EmptyIfInvisibleContainer

This widget acts like a standard wrapper container, with the special case that if either its contents is empty or invisible, then it will report its own size as zero.

UIBackingBox

This widget acts like a standard UIBox, with the added functionality of consuming all mouse click events targeted within its area. This prevents mouse click events from propagating to layers beneath the box.

UILabelledIcon

This widget allows the user to display an icon alongside a descriptive label, such as might be used in a HUD to display brief player statistics, The icon can be placed either to the left or the right of the label.

Testing

• There are some basic test screens for this in my temporary nuiExperiments module. You'll need to fetch that into your workspace first. When asked to open a screen, open it using the showNUIScreen <screenUrn> command.

  EmptyIfInvisibleContainer

• Open the nuiExperiments:emptyIfInvisibleContainers screen.
• Toggle the Show checkbox off.
• One of the buttons should become invisible.
• When the button is invisible, all adjacent buttons should shift along to fill the space previously occupied by that button.
• Toggle the Show checkbox on.
• One of the buttons should become visible again.

UIBackingBox

• Open the nuiExperiments:uiBackingBoxes screen.
• Try clicking on the background (outside of any boxes). The background click counter should increase.
• Try clicking on the blue box. The background click counter should still increase.
• Try clicking on the black box. The background click counter should not increase.

UILabelledIcon

• Open the nuiExperiments:uiLabelledIcons screen.
• There should be three labels present. One with an icon to the left of it, the other with an icon to its right and at the top a label with no icon associated.

Notes

• The UIBackingBox test is unlikely to succeed without #663, since it fixes mouse events previously not being consumed.
• The game may crash when closing a screen with the escape key. This is an unrelated issue regarding NUI screens outside of the engine not being correctly injected.