[Divider] Allow divider drag handle overlay on primary container

Adjust the computation of the divider surface bounds so that the drag
handle can be placed on top of the primary container when the divider
width is less than the drag handle size.

Bug: 327067596
Test: atest DividerPresenterTest
Change-Id: I71fd03a0e7351a68585d2cd30077a8a26adea752