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/anyref-param.wat

@@ -0,0 +1,37 @@
+;; @xform export "foo" (externref_borrowed)
+
+(module
+  (func $foo (export "foo") (param i32))
+  (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 (param i32)))
+  (type (;1;) (func (param externref)))
+  (func $foo externref shim (type 1) (param externref)
+    (local i32)
+    global.get 0
+    i32.const 1
+    i32.sub
+    local.tee 1
+    global.set 0
+    local.get 1
+    local.get 0
+    table.set 0
+    local.get 1
+    call $foo
+    local.get 1
+    ref.nullextern
+    table.set 0
+    local.get 1
+    i32.const 1
+    i32.add
+    global.set 0)
+  (func $foo (type 0) (param i32))
+  (table (;0;) 32 externref)
+  (global (;0;) (mut i32) (i32.const 32))
+  (export "foo" (func $foo externref shim)))
+;)