Custom binary XML wire protocol.

We've identified that XML writing and reading uses roughly 1.5% of
all system_server CPU, and can generate many temporary objects.

Building on the recent TypedXmlSerializer/PullParser interfaces, this
change introduces new BinaryXmlSerializer/PullParser implementations
that store data using a custom binary wire protocol.  Benchmarking of
a typical packages.xml has shown this new binary approach can write
4.3x faster and read 8.5x faster, while using 2.4x less disk space:

    timeWrite_Fast_mean: 27946635
    timeWrite_Binary_mean: 6519341

    timeRead_Fast_mean: 59562531
    timeRead_Binary_mean: 7020185

A major factor in choosing to invest in this new wire protocol is
that it enables the long-tail of over 100 unique XML schemas used
across the OS internals to be transparently upgraded to gain these
benefits with only minimal changes, reducing the risks associated
with rewriting those schemas.

Finally, since the wire protocol is essentially a serialized event
stream, it's trivial to transparently convert this new protocol
into human-readable XML and vice-versa.  The tests in this change
demonstrate this translation working correctly, and future changes
will introduce new shell tools to aid development work.

Bug: 171832118
Test: atest FrameworksCoreTests:android.util.XmlTest
Test: atest FrameworksCoreTests:android.util.BinaryXmlTest
Test: atest CorePerfTests:android.util.XmlPerfTest
Change-Id: Ib9390701f09562dca952b3786622675b9c68a462