Fix Character.getDirectionality.

Previously we'd throw ArrayIndexOutOfBoundsException for U+2066..U+2069.
Now we'll return DIRECTIONALITY_UNDEFINED. I've exposed (via @hide) the
underlying icu4c implementation so that frameworks code at least can work
with the new explicit bidi formatting characters.

Bug: 15492712
Change-Id: I96583c7e1c6be26d3f1a857615a1042d58e9feaf
Merge "Fix Character.getDirectionality."
Add FLOAT entry to EmptyArray

Change-Id: I70a591093557ce3dd0471bcc7e888d630c80bb88
Merge "Add FLOAT entry to EmptyArray"