flamenco, vm: syscall err code refactor

[ravyu-jump]

README

Highly, HIGHLY recommend reviewing this in individual commits, especially commits 2 and 3. This is a (largely) cosmetic PR, so diffs are going to look horrendous if looked all at once.
For your convenience:

• Commit 1
  • Renames FD_VM_ERR_SYSCALL* to FD_VM_SYSCALL_ERR* for clarity
  • Convert VM errors emitted in syscall implementations to Syscall errors, potentially creating new, duplicate syscall errors if necessary
  • Cleanup unused errors
  • Update documentation
• Commit 2
  • Completes error type conversion for syscall-specific macros defined in flamenco/vm/fd_vm_private.h
  • Completes cleanup
• Commit 3
  • Moves syscall-specific macros in flamenco/vm/fd_vm_private.h to a new file flamenco/vm/syscall/fd_vm_syscall_macros.h
  • Update documentation

Motivation

SIMD-0182* requires us to distinguish syscall errors from non-syscall errors during VM execution. We thus want to have a separate set of error codes for errors that occur inside syscalls, even if they are technically VM errors (i.e., segfaults, compute budget overruns, etc.,).

I also took this opportunity to move certain Syscall-specific VM interfacing macros that were defined in fd_vm_private.h to a new folder within flamenco/vm/syscalls so that the scope of these macros are clearly defined (i.e., to be used within Syscalls only). This clearly delineates where syscall and VM error codes are emitted.

*this is not an implementation of SIMD-0182, rather a pre-requisite