Improve A2DP codec run-time debug-abilitity

Rename A2DP_DumpCodecInfo() to A2DP_CodecInfoString() and change
the usage. Previously, A2DP_DumpCodecInfo() would print the
the codec information only if LOG_VERBOSE() was enabled in compile time.
The new A2DP_CodecInfoString() now returns human-readable std::string
with the codec information.
That string can be used in debug log messages that can be enabled
in run-time.

Bug: 77525584
Test: Manual - Examine log messages when A2DP streaming with and
      without debug log messages enabled.

Change-Id: Idd440d6c9e908520132feeeb5388d3e6aefa26db