bluez5: split A2DP codecs to separate SPA plugins
Make easier to package A2DP codecs separately, by splitting each to a separate SPA plugin. Adjust the code to not use a global variable for the codec list.
The A2DP SPA interface API is in the bluez5 private headers, and not exposed in installed SPA headers, as it's too close to the implementation.
spa/support: add plugin loader interface
Add a SPA interface for loading SPA plugins, so that plugins can request the host to load other plugins.
context: add SPA plugin loader interface to support plugins
Edited by P V