Audio V4: Implement the shim core 4.0 -> legacy

All the new files added are a copy of the 2.0 ones, with just the
version 2 that was changed to 4.

Due to the rollback on the retrocompatiblity breakage,
the split of implementation is not strictly needed any more.
This makes the current split in .impl.h and double include
unnecessary complicated.
This will need to be factorized in a future patch.

Bug: 38184704
Test: compile
Change-Id: I0d699ade7558ed68125b300f8522e2767ae1ee37
Merged-In: I0d699ade7558ed68125b300f8522e2767ae1ee37
Cherry-picked from master
Signed-off-by: Kevin Rocard <krocard@google.com>