add async function syntax

...functions/syntax/async-class-decl-private-method.template

...ns/syntax/async-class-decl-static-private-method.template

...functions/syntax/async-class-expr-private-method.template

...ns/syntax/async-class-expr-static-private-method.template

...nerators/default/async-class-decl-private-method.template

...s/default/async-class-decl-static-private-method.template

...nerators/default/async-class-expr-private-method.template

...s/default/async-class-expr-static-private-method.template

src/generators/default/class-decl-private-method.template

...erators/default/class-decl-static-private-method.template

src/generators/default/class-expr-private-method.template

...erators/default/class-expr-static-private-method.template