Implement persistentScrollbar for ScrollView

[CarpeDiEmma]

Creating an issue here per @acoates-ms to implement persistentScrollbar to allow for the scrollbar to remain visible outside of actively scrolling.

[chrisglein]

@CarpeDiEmma Do you have non-RNW native scroll bars you're forcing to show? If so, is that handled per instance or on a global app level.

As for this setting, yep it's a gap and should be implemented.
https://reactnative.dev/docs/virtualizedlist#persistentscrollbar

[CarpeDiEmma]

@chrisglein Not me in particular--I have been primarily working in RNW. From a quick glance around the xaml in the Xbox Shell Apps, the configuration is handled per instance. Also the "type" of scrollview also determines whether it is consistently shown or not--a right stick scroll bar scroll viewer will always have the scroll bar as persistent, whereas a left stick scroll bar scroll viewer may not.

[haightt]

Does this prop not work for any of the virtualized lists in RNW?

[chrisglein]

Not something we plan to address on the Paper renderer as we move towards Fabric.
Fabric API completion is tracked here: #11152