Enable the gc-copying cargo feature by default (#13234)

Now that it isn't just a skeleton.

Author: fitzgen

Cargo.toml

@@ -506,6 +506,7 @@ default = [
   "component-model-async",
   "threads",
   "gc",
+  "gc-copying",
   "gc-drc",
   "gc-null",
   "stack-switching",

crates/wasmtime/Cargo.toml

@@ -134,6 +134,7 @@ default = [
   'backtrace',
   'cache',
   'gc',
+  'gc-copying',
   'gc-drc',
   'gc-null',
   'wat',