Move shaping to native.

Add internal API (getTextRunAdvances) to Paint, use when measuring.
Add internal API (getTextRunCursor) to Paint, use when determining
valid cursor positions.

Remove java-level shaping code.  Remove 'prep' code in TextLine
(except for replacement text) since shaping now is done on the fly as
needed in native.

Provide explicit shaping context bounds to internal text measuring,
cursor movement, and rendering APIs.

Update for to changes in external API in ushape.h.

Change-Id: I146958b624802ce8553125e5c3c6c03031bc9608