Add asyng-gen templates for params in the test gen tool

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

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

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

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

src/params/default/cls-decl-async-gen-meth-static.template

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

src/params/default/cls-expr-async-gen-meth-static.template

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

src/params/error/async-gen-func-decl.template

src/params/error/async-gen-func-expr.template

src/params/error/async-gen-meth.template

src/params/error/async-gen-named-func-expr.template

src/params/error/cls-decl-async-gen-meth-static.template

src/params/error/cls-decl-async-gen-meth.template

src/params/error/cls-expr-async-gen-meth-static.template

src/params/error/cls-expr-async-gen-meth.template

src/params/syntax/async-gen-func-decl.template

src/params/syntax/async-gen-func-expr.template

src/params/syntax/async-gen-meth.template

src/params/syntax/async-gen-named-func-expr.template