Fix async generator test templates

- Insert a missing .next() call
- Avoid overlapping names used in test cases

Case files like `src/dstr-binding/ary-ptrn-elem-ary-elision-init.case` are already setting
bindings named `g`. Renaming them in the templates prevents overlapping names.

src/dstr-binding/default/async-gen-func-named-expr-dflt.template

@@ -19,7 +19,7 @@ flags: [async]
 
 var callCount = 0;
 var f;
-f = async function* g(/*{ elems }*/ = /*{ vals }*/) {
+f = async function* h(/*{ elems }*/ = /*{ vals }*/) {
   /*{ body }*/
   callCount = callCount + 1;
 };

src/dstr-binding/default/async-gen-func-named-expr.template

@@ -19,7 +19,7 @@ flags: [async]
 
 var callCount = 0;
 var f;
-f = async function* g(/*{ elems }*/) {
+f = async function* h(/*{ elems }*/) {
   /*{ body }*/
   callCount = callCount + 1;
 };

src/dstr-binding/default/cls-decl-async-gen-meth.template

@@ -48,6 +48,6 @@ class C {
   }
 };
 
-new C().method(/*{ vals }*/).then(() => {
+new C().method(/*{ vals }*/).next().then(() => {
     assert.sameValue(callCount, 1, 'invoked exactly once');    
 }).then($DONE, $DONE);

src/dstr-binding/error/async-gen-func-named-expr-dflt.template

@@ -17,7 +17,7 @@ info: |
 ---*/
 
 var f;
-f = async function* g(/*{ elems }*/ = /*{ vals }*/) {
+f = async function* h(/*{ elems }*/ = /*{ vals }*/) {
   /*{ body }*/
 };