ZStackLayout

[sjordanGSS]

Opening a discussion about the ZStackLayout feature detailed here: #2115 to avoid further clogging the PR with feedback.

Personally I'm rather looking forward to this feature, I have a number of views that take the form

<Grid>
<SomethingLayout />
<ActivityIndicator />
</Grid>

so being able to replace the outer Grid with a layout designed specifically for this job is going to make my code much neater and easier to understand at a glance. From the current state of the PR I'm expecting this to look something like

<ZStackLayout>
<SomethingLayout />
<ActivityIndicator />
</ZStackLayout>

I'm also looking forward to how this might interact with FlexLayout to allow views to be overlapped inside the layout without resorting to more unnecessary Grids.