Improve type imports into components (#5777)

This commit fixes a panic related to type imports where an import of a
type didn't correctly declare the new type index on the Wasmtime side of
things. Additionally this plumbs more support throughout Wasmtime to
support type imports, namely that they do not need to be supplied
through a `Linker`. This additionally implements a feature where empty
instances, even transitively, do not need to be supplied by a Wasmtime
embedder. This means that instances which only have types, for example,
do not need to be supplied into a `Linker` since no runtime information
for them is required anyway.

Closes #5775

tests/misc_testsuite/component-model/import.wast

@@ -3,3 +3,18 @@
     (import "host-return-two" (func $f (result u32)))
     (export "x" (func $f)))
   "component export `x` is a reexport of an imported function which is not implemented")
+
+(assert_invalid
+  (component
+    (import "host-return-two" (instance))
+  )
+  "expected instance found func")
+
+;; empty instances don't need to be supplied by the host, even recursively
+;; empty instances.
+(component
+  (import "not-provided-by-the-host" (instance))
+  (import "not-provided-by-the-host2" (instance
+    (export "x" (instance))
+  ))
+)

tests/misc_testsuite/component-model/linking.wast

@@ -2,7 +2,7 @@
   (component
     (import "undefined-name" (core module))
   )
-  "import `undefined-name` not defined")
+  "expected module found nothing")
 (component $i)
 (component
   (import "i" (instance))
@@ -15,4 +15,4 @@
   "expected func found instance")
 (assert_unlinkable
   (component (import "i" (instance (export "x" (func)))))
-  "export `x` not defined")
+  "expected func found nothing")

tests/misc_testsuite/component-model/types.wast

@@ -320,3 +320,17 @@
 
   (instance $c (instantiate $c (with "x" (component $x))))
 )
+
+(component
+  (type $t1 u64)
+  (import "a" (type $t2 (eq $t1)))
+  (import "b" (type $t3 (eq $t2)))
+)
+
+(component
+  (import "a" (instance
+    (type $t1 u64)
+    (export $t2 "a" (type (eq $t1)))
+    (export "b" (type (eq $t2)))
+  ))
+)