module-linking: Implement outer module aliases (#2590)

This commit fully implements outer aliases of the module linking
proposal. Outer aliases can now handle multiple-level-up aliases and now
properly also handle closed-over-values of modules that are either
imported or defined.

The structure of `wasmtime::Module` was altered as part of this commit.
It is now a compiled module plus two lists of "upvars", or closed over
values used when instantiating the module. One list of upvars is
compiled artifacts which are submodules that could be used. Another is
module values that are injected via outer aliases. Serialization and
such have been updated as appropriate to handle this.

crates/jit/src/instantiate.rs

@@ -221,7 +221,7 @@ impl CompiledModule {
         artifacts: Vec<CompilationArtifacts>,
         isa: &dyn TargetIsa,
         profiler: &dyn ProfilingAgent,
-    ) -> Result<Vec<Self>, SetupError> {
+    ) -> Result<Vec<Arc<Self>>, SetupError> {
         maybe_parallel!(artifacts.(into_iter | into_par_iter))
             .map(|a| CompiledModule::from_artifacts(a, isa, profiler))
             .collect()
@@ -232,7 +232,7 @@ impl CompiledModule {
         artifacts: CompilationArtifacts,
         isa: &dyn TargetIsa,
         profiler: &dyn ProfilingAgent,
-    ) -> Result<Self, SetupError> {
+    ) -> Result<Arc<Self>, SetupError> {
         // Allocate all of the compiled functions into executable memory,
         // copying over their contents.
         let (code_memory, code_range, finished_functions, trampolines) = build_code_memory(
@@ -266,7 +266,7 @@ impl CompiledModule {
 
         let finished_functions = FinishedFunctions(finished_functions);
 
-        Ok(Self {
+        Ok(Arc::new(Self {
             module: Arc::new(artifacts.module.clone()),
             artifacts,
             code: Arc::new(ModuleCode {
@@ -275,7 +275,7 @@ impl CompiledModule {
             }),
             finished_functions,
             trampolines,
-        })
+        }))
     }
 
     /// Crate an `Instance` from this `CompiledModule`.