Mass rename anyref to externref (#2142)

Updates a mess of dependencies and tracks the most recent version of the
reference types specification.

crates/externref-xform/tests/import-anyref-owned.wat

@@ -0,0 +1,31 @@
+;; @xform import "" "a" (externref_owned)
+
+(module
+  (import "" "a" (func $a (param i32)))
+  (func (export "foo")
+    i32.const 0
+    call $a)
+  (func $alloc (export "__externref_table_alloc") (result i32)
+    i32.const 0)
+  (func $dealloc (export "__externref_table_dealloc") (param i32))
+)
+
+(; CHECK-ALL:
+(module
+  (type (;0;) (func))
+  (type (;1;) (func (param i32)))
+  (type (;2;) (func (param externref)))
+  (import "" "a" (func $a (type 2)))
+  (func $a externref shim (type 1) (param i32)
+    local.get 0
+    table.get 0
+    local.get 0
+    call $dealloc
+    call $a)
+  (func (;2;) (type 0)
+    i32.const 0
+    call $a externref shim)
+  (func $dealloc (type 1) (param i32))
+  (table (;0;) 32 externref)
+  (export "foo" (func 2)))
+;)