Fix RenderArea use after free error

When RenderEngine is single threaded, renderScreenImpl immediately calls present instead of moving it into the returned future. This caused the unique_ptr<RenderArea> to be destroyed when renderScreenImpl returned, deleting RenderArea prematurely. We can use a shared_ptr to ensure that RenderArea is only deleted once both captureScreenCommon and present no longer need it.

Bug: 264827546
Test: atest ScreenCaptureTest
Test: go/wm-smoke
Change-Id: I8b591bec7c6ad07df9fa9b7f62495dac10a68a93