Support custom render quantum size

[orottier]

On hold for now at the W3C WG: WebAudio/web-audio-api#2469

• Remove 128 from public AudioProcessor API Prepare public API for variable render quantum size #242
• Enable variable buffer size in AudioRenderQuantum allocator WIP: Remove hardcoded RENDER_QUANTUM_SIZE from Allocator #279
• Pass hardware buffer quantum size to audio graph, expose AudioContextOption
• Implement variable render quantum size for easy AudioNodes
• Implement variable render quantum size for hard AudioNodes (Analyser, Convolver, ..)