Camera: Add logic to switch between vendor and fallback extension impl

- Enables extensions to switch to a fallback software implementation
if the vendor does not support an extension that is equipped with a
fallback
- Changes the way extensions connect to the proxy service by enabling
a connection per extension. This allows multiple proxy service
connections simultaneously.

Test: Camera CTS Test
Bug: 302582551
Change-Id: I25b4ee7089e4c1e83cde51854322f32d4176e8bb