[risk=low][RW-7896] HTMLViewer: detect end of scrolling by 10% visibility of last document element (#6341)
[risk=low][RW-7896] HTMLViewer: detect end of scrolling by 10% visibility of last document element (#6341)

* Previous version required 100% visibility of element which was sometimes off-screen
all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench,all-of-us/workbench