AutoTranslate: Pad view text for compatibility reasons.

Some apps operate on the view text based on layout calculations made on
the transformed text. This can cause issues (even crashes) if the
transformed text is longer than the original, as is often the case with
Translate. A previous temporary fix,
I685ae4a9752c817db81f0d736f1d746b2e4a9839, ellipsized the translated
text. This change fixes it properly by instead padding the original
text.

A followup change will make this controllable by API instead of padding
every TextView.

The en space character, U+2002, is used for the padding here. It seems
to work well in practice for multiple languages. We don't make this
configurable through API as it could make debugging harder (issues
triggered by server-side changes).

Bug: 179693024
Test: atest CtsTranslationTestCases
Test: manual - toggling between original and translated, scrolling, new
 views appearing, multiple apps
Change-Id: I9d7db5d2bc200e4042baf3267796f00cfc298f19