wasmtime: Refactor how imports are resolved (#2102)

This commit removes all import resolution handling from the
`wasmtime-jit` crate, instead moving the logic to the `wasmtime` crate.
Previously `wasmtime-jit` had a generic `Resolver` trait and would do
all the import type matching itself, but with the upcoming
module-linking implementation this is going to get much trickier.

The goal of this commit is to centralize all meaty "preparation" logic
for instantiation into one location, probably the `wasmtime` crate
itself. Instantiation will soon involve recursive instantiation and
management of alias definitions as well. Having everything in one
location, especially with access to `Store` so we can persist
instances for safety, will be quite convenient.

Additionally the `Resolver` trait isn't really necessary any more since
imports are, at the lowest level, provided as a list rather than a map
of some kind. More generic resolution functionality is provided via
`Linker` or user layers on top of `Instance::new` itself. This makes
matching up provided items to expected imports much easier as well.

Overall this is largely just moving code around, but most of the code
in the previous `resolve_imports` phase can be deleted since a lot of it
is handled by surrounding pieces of `wasmtime` as well.

crates/runtime/src/instance.rs

@@ -897,28 +897,36 @@ impl InstanceHandle {
         };
         let instance = handle.instance();
 
+        debug_assert_eq!(vmshared_signatures.len(), handle.module().signatures.len());
         ptr::copy(
             vmshared_signatures.values().as_slice().as_ptr(),
             instance.signature_ids_ptr() as *mut VMSharedSignatureIndex,
             vmshared_signatures.len(),
         );
+        debug_assert_eq!(imports.functions.len(), handle.module().num_imported_funcs);
         ptr::copy(
-            imports.functions.values().as_slice().as_ptr(),
+            imports.functions.as_ptr(),
             instance.imported_functions_ptr() as *mut VMFunctionImport,
             imports.functions.len(),
         );
+        debug_assert_eq!(imports.tables.len(), handle.module().num_imported_tables);
         ptr::copy(
-            imports.tables.values().as_slice().as_ptr(),
+            imports.tables.as_ptr(),
             instance.imported_tables_ptr() as *mut VMTableImport,
             imports.tables.len(),
         );
+        debug_assert_eq!(
+            imports.memories.len(),
+            handle.module().num_imported_memories
+        );
         ptr::copy(
-            imports.memories.values().as_slice().as_ptr(),
+            imports.memories.as_ptr(),
             instance.imported_memories_ptr() as *mut VMMemoryImport,
             imports.memories.len(),
         );
+        debug_assert_eq!(imports.globals.len(), handle.module().num_imported_globals);
         ptr::copy(
-            imports.globals.values().as_slice().as_ptr(),
+            imports.globals.as_ptr(),
             instance.imported_globals_ptr() as *mut VMGlobalImport,
             imports.globals.len(),
         );