adb: add IOVector.

An IOVector is a collection of immutable reference counted blocks which
can have its head detached at an arbitrary index. This is extremely
useful for implementing packet-framed protocols like adb on top of a
stream protocol like TCP: a stream reader can read blocks, append them
to the end of the IOVector, and then pull packets off of the front.
This also lends itself naturally towards scatter/gather I/O, which will
enable us to read data from disk and send it across the wire with a
theoretical minimum number of copies in USB, and one extra copy over
TCP.

Since this is basically a generalization of std::deque<Range>, delete
Range and replace its uses with IOVector.

Test: adb_test
Test: wine adb_test.exe
Change-Id: I06561ad0bb25a3a51b378b61d257b5b04b41d9c4