Where are the image and sound files inside XCode?-Collection of common programming errors

They are compiled into the lib as a byte code which is then interpreted at runtime. Disclosure of this would destroy Unity’s business model, as everyone would make corrections into unity-produced code. It is more easy for them to interpret bytecode rather than translating it into human-readable language like C or objective-c.

The answer is: yes, they are compiled into lib.

If you want to access them from objective-c layer, you have to add them to project again in a usual xCode way ,so their data will be doubled in the project.