Allow the const keyword in parameters

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const function parameters

Note: this is a cross-post from https://discourse.wicg.io/t/js-const-function-parameters/1927 let creates a mutable binding, and const creates an immutable binding. However function parameters are always implicity mutable, i.e.: function foo(param) // 'param' is implicitly mutable { console.log("param = " + param); param = 5; // this is allowed console.log("param = " + param); }; Why not allow const in function parameters? function foo(const param) // 'param' is immutable { …