Remove depth argument from InlineInfo accessors in stack maps.

The InlineInfo class actually represented a list of inlining
information for a given stack map, and the depth argument was
used everywhere to select to desired element from the list.
This was verbose and inconsistent with the other classes.

Change the InlineInfo class to represent a single inlining,
and select the desired depth when getting it from CodeInfo.

Test: test-art-host-gtest-stack_map_test
Change-Id: I35b73e6704854f0203f51d4dbdbed5b1d1cd5a3b