Add tests for default parameters

src/dflt-params/abrupt.case

src/dflt-params/arg-val-not-undefined.case

src/dflt-params/arg-val-undefined.case

src/dflt-params/default/arrow-function.template

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

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

src/dflt-params/default/cls-decl-meth-static.template

src/dflt-params/default/cls-decl-meth.template

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

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

src/dflt-params/default/cls-expr-meth-static.template

src/dflt-params/default/cls-expr-meth.template

src/dflt-params/default/func-decl.template

src/dflt-params/default/func-expr.template

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

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

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

src/dflt-params/default/meth.template

src/dflt-params/duplicates.case

src/dflt-params/error/arrow-function.template