BUG-5561: retain SchemaContext order for bits

This patch reworks BitsCodec so it retains the bit order
defined in SchemaContext, which by extension means the values
coming from Binding objects should end up being sorted
by position.

Change-Id: Ice154dd7e38e6b213c281ddb492408f619e3a5f8
Signed-off-by: Robert Varga <rovarga@cisco.com>
(cherry picked from commit 85945172d532b22797b0f1786dbf448c63b66f63)