Floss: stub non-standard codecs

Each of these non-standard codec has its own intricacies in their
terms, while some of them will be enabled gradually.

In this CL, we stub the implementations of each vendor codec as an
alternative to using build flags to decide which can be built.

Bug: 268424393
Tag: #floss
Test: atest net_test_stack_a2dp_native
Change-Id: Ic79879821b1478511c040704f255329090f28452