Move getText from dm.Document to ElementLinearData

Also add 'maintainIndices' flag which pads out element data
with line breaks so offsets can be easily mapped between
the data the string.

Change-Id: If41f10bf013641d693c074a6eed6d172a1340bc7
Emit ce.Surface#position after dm.Surface#documentUpdate

Change-Id: I8372fa0eaaef41cf3b6182b756ba94f9711c7205
Merge "Move getText from dm.Document to ElementLinearData"
Merge "Emit ce.Surface#position after dm.Surface#documentUpdate"