Fix module-linking handling of instance subtypes (#2466)

* Fix module-linking handling of instance subtypes

When we alias the nth export of an instance, due to subtyping the nth
export may not actually be what we want. Instead we need to look at our
local type definition's nth export's name, and lookup that name off the
export.

* Update crates/wasmtime/src/instance.rs

Co-authored-by: Peter Huene <peter@huene.dev>

Co-authored-by: Peter Huene <peter@huene.dev>

tests/misc_testsuite/module-linking/instantiate.wast

@@ -233,3 +233,52 @@
     (import "b" "i" (instance (export "" (func))))
   )
   "instance types incompatible")
+
+;; ensure we ignore other exported items
+(module $b
+  (module $m
+    (func (export "f") (result i32)
+      i32.const 300)
+    (global (export "g") i32 (i32.const 0xfeed))
+  )
+
+  (instance (export "i") (instantiate 0))
+)
+(module
+  (import "b" "i" (instance $i
+    (export "g" (global $g i32))
+  ))
+
+  (func (export "get") (result i32)
+    global.get $i.$g)
+)
+(assert_return (invoke "get") (i32.const 0xfeed))
+
+;; ensure the right export is used even when subtyping comes into play
+(module $b
+  (module $m
+    (func (export "f") (result i32)
+      i32.const 300)
+    (func (export "g") (param i32) (result i32)
+      i32.const 100
+      local.get 0
+      i32.add)
+  )
+
+  (instance (export "i") (instantiate 0))
+)
+(module
+  (import "b" "i" (instance $i
+    ;; notice that this order is swapped
+    (export "g" (func $g (param i32) (result i32)))
+    (export "f" (func $f (result i32)))
+  ))
+
+  (func (export "f") (result i32)
+    call $i.$f)
+  (func (export "g") (param i32) (result i32)
+    local.get 0
+    call $i.$g)
+)
+(assert_return (invoke "f") (i32.const 300))
+(assert_return (invoke "g" (i32.const 3000)) (i32.const 3100))