Add async generator templates for the arguments cases

src/arguments/default/async-gen-func-decl.template

src/arguments/default/async-gen-func-expr.template

src/arguments/default/async-gen-meth.template

src/arguments/default/async-gen-named-func-expr.template

...arguments/default/cls-decl-async-gen-meth-static.template

src/arguments/default/cls-decl-async-gen-meth.template

...arguments/default/cls-expr-async-gen-meth-static.template

src/arguments/default/cls-expr-async-gen-meth.template