Let's use shared_ptr since manual ref counting can be a bug-prone and
using the global mutex inside destructor is not useful for some time.

To remove raw pointer manipulation, needed to change Layout
constructors. Layout is no longer copyable and need to pass
FontCollection to constructor.

Bug: 28119474
Test: minikin_tests passed
Test: hwui_unit_tests passed
Test: No performance regression in minikin_perftest.
Change-Id: I8824593206ecba74cbc9731e298f045e1ae442a3