RigVM.Compiler.AllowCallableFallbackToInlining

When RigVM.Compiler.CompileFunctionsToCallables is on and a function reference cannot be lowered to a callable, allow the compiler to silently fall back to function-reference inlining. Disable (set to 0) for unit tests that need to verify the callable-lowering path is actually exercised — those tests will then fail the compile instead of passing via the inline path.