Codegen Templates for Source Effects, Submix Effects, and Synthesizers needs updating

Code gen templates need to be updated according to changes made to the OnGenerateAudio API.

1. Create an AudioMixer Enabled C++ Project
2. Add New > New C++ Class
3. Click Show All Classes as TRUE
4. Search "SynthComponent"
5. Create a new SynthComponent child class

Expected: Code will compile and new SynthComponent is available in the project

Result: Code does not compile because OnGenerateAudio function is the wrong type.