cranelift-module: expose trap information when defining functions

The current interface of `cranelift-module` requires consumers who want
to be informed about traps to discover that information through
`Module::Product`, which is backend-specific.  Since it's advantageous
to manipulate this information in a backend-agnostic way, this patch
changes `Module::define_function{,_bytes}` to return information about
the traps contained in the function being defined.

cranelift/module/src/backend.rs

@@ -86,7 +86,7 @@ where
         ctx: &Context,
         namespace: &ModuleNamespace<Self>,
         code_size: u32,
-    ) -> ModuleResult<Self::CompiledFunction>;
+    ) -> ModuleResult<(Self::CompiledFunction, Option<&Vec<TrapSite>>)>;
 
     /// Define a function, taking the function body from the given `bytes`.
     ///
@@ -98,7 +98,7 @@ where
         bytes: &[u8],
         namespace: &ModuleNamespace<Self>,
         traps: Vec<TrapSite>,
-    ) -> ModuleResult<Self::CompiledFunction>;
+    ) -> ModuleResult<(Self::CompiledFunction, Option<&Vec<TrapSite>>)>;
 
     /// Define a zero-initialized data object of the given size.
     ///