Add architecture-independent exception handling APIs sufficient for hyperlight-wasm

[syntactically]

Currently, hyperlight-guest exposes an architecture-specific way of overriding certain raw exception handler on x86-64 that is used by hyperlight-wasm. Really, we should instead have architecture-independent hooks for

• Intercepting certain kinds of misbehaviour-indicating exceptions (e.g. FP divide by zero, access to guard regions)
• Support for the virtual memory primitives that hyperlight-wasm needs in hyperlight-guest (e.g. zero-on-first-read regions, copy-on-write images, guard regions)