Add A2DP/SDP fuzzers for bt-stack

Added Libfuzzer fuzzers for both the A2DP and SDP components of
bt-stack. Fuzzers will call exposed API functions with random
order/parameters. Note that as some of these components fight with
libfuzzer for signal handlers, it's recommended to run these with
the following env_vars:
  HWASAN_OPTIONS='handle_abort=2 handle_segv=1 allocator_may_return_null=1'

Test: Tested each fuzzer for a few million iterations without
      fuzzer-side crashes. Execs/s are approximately in the 50-250
      range after coverage is established (all fuzzers running on a
      single device).
Signed-off-by: Michael Ensing <michael.ensing@leviathansecurity.com>
Change-Id: Ib40c39fd4bc77a97310ee0e550b19bafbbb7057e