Skip Class::GetDefaultFieldValue when the xref is not a function entry

[Joshtt23]

Summary

• On some Unity 6 IL2CPP builds, FindClassGetFieldDefaultValueXref lands on an unaligned epilogue (a jmp into the ret path), not Class::GetDefaultFieldValue.
• Detouring that address aborts the CLR (0x80131506).
• Keep the existing First/Last / [^2] heuristic when that pointer is 16-byte aligned. Otherwise pick another aligned jump target, or skip this hook only with a warning (no throw).
• Same alignment rule as imageGetTypeXrefs in MetadataCache_GetTypeInfoFromTypeDefinitionIndex_Hook.
• Signature-based finds are unchanged. This does not skip every unaligned hook in Hook.ApplyHook.

Test plan

• Games where the current xref is already aligned: hook still applies.
• Unity 6 IL2CPP where the xref is an interior/epilogue address: log a warning, chainloader completes, other hooks still apply.
• Injected enum field defaults may be unavailable when this hook is skipped (same as not finding the method).

Runtime-tested on Unity 6000.3.15x1 / metadata 39 (Rust client). Class::Init is a separate change (#277).