New parameters structure

[isanae]

The problem this is trying to solve is that the old USVSParameters structure, USVFSInitParameters() and USVFSUpdateParams() can't be modified without breaking the ABI. I wanted to add the spawn delay parameter, but then the DLL wouldn't be compatible with 2.2.1. I don't want to pick and choose changes to release patches to usvfs.

This PR completely deprecates USVSParameters as well as its associated functions, and changes all the internals to use the new usvfsParameters instead. The two structures are basically identical (except for the new spawn delay), but usvfsParameters is not exposed, it's just an opaque pointer. It also starts a long-term process of adding the usvfs prefix to the public interface, because stuff like GetLogMessages() isn't great.

Specifically, these are deprecated:

• ConnectVFS(), replaced by usvfsConnectVFS().
• CreateVFS(), replaced by usvfsCreateVFS().
• USVFSInitParameters(), replaced by usvfsCreateParameters() and its associated functions.
• USVFSUpdateParams(), replaced by usvfsUpdateParameters()
• USVSParameters structure, replaced by usvfsParameters
• CreateHookContext(), replaced by usvfsCreateHookContext() (seems to be only used for internal tests)