Add a standardized shared memory type

This adds a simple SharedFileRegion type that can be used to pass blocks
of shared memory between processes in a structured AIDL interface.

In addition a small utility library is provided for interfacing with
existing code that uses IMemory.

The intention is to add utilities for direct usage of the memory
content.

Bug: 160253486
Test: Ran the included unit test. Integration testing as part of whole
      topic tests via the audio effect tests.
Change-Id: I3f923047e364ba44fda316bdd563561ebec201b2