ISSUE-144101: change children size calculation

There is loss of accuracy, when users passed large span count to
GridLayoutManager's constructor.
And RecyclerView size became smaller, then users expect.

Change-Id: Id2fd03285e9bec7b2ed439f1c0ef8a3ddfcecdc4
ISSUE-144101: calculate all items borders
ISSUE-144101: optimize code
ISSUE-144101: add tests
ISSUE-144101: adjust lines size
2 files changed