Enable nested bidi levels in a paragraph.

Changes the internal representation of direction information in the Directions object to be a visually-ordered list of start/length+direction pairs instead of a list of directionality inversion offsets.

Rewrite Layout.getOffsetToLeft/RightOf to use run information instead of width metrics.

Remove java Bidi, use native.  Switch bidi tests to test native, expect levels instead of dirs.

Add test of directionality.  Leave in switch to turn new code off and restore previous behavior for now.

Change-Id: Iea8bb46c678a18820e237c90f76007a084c83051