Prepare for binary XML pivot.

As part of preparing to enable the new binary XML wire format across
the device, we ran a large suite of unit tests which uncovered a
handful of bugs where client code was assuming that the serializer
would create TEXT tokens for newlines between tags.

Also relaxes all binary XML classes to accept either "UTF-8" or
"utf-8" as the encoding name.  Slight bug fixes to clear names, text,
and attributes for each event to match XmlPullParser documentation.

Fixes for existing unit tests that were assuming human-readable XML,
or assuming that the serialization would perform UTF-8 validation.

Bug: 171832118
Test: atest FrameworksServicesTests
Change-Id: I841fe41e4967b36ab17551294ae0f42fb87a8e71