Support renaming properties in in expressions

[andrewiggins]

Adds a BinaryExpression visitor that renames string literal properties used with the in operator (e.g., 'foo' in obj → '__FOO__' in obj).

This change aims to match Terser's behavior here. Put the following options and example code in the Terser REPL to see it's behavior.

Options

// edit terser options
{
  module: true,
  compress: {},
  mangle: {
    properties: {
      regex: "^_[^_]"
    }
  },
  output: {},
  parse: {},
  rename: {},
  nameCache: {
    props: {
      "cname": 6,
      "props": {
        "$_prop1": "p1"
      }
    }
  }
}

Input

export const obj = {};

// Does transform
console.log("_prop1" in obj);
console.log('_prop1' in obj);
console.log(`_prop1` in obj);

// Does not transform
const s = "_prop1";
console.log(s); // Note: it will transform if you remove this line as it'll inline `s`
console.log(s in obj);
console.log("_prop2" in obj);

Expected Output

Note: newlines added by me for easier reading.

export const obj={};
console.log("p1"in obj),
console.log("p1"in obj),
console.log("p1"in obj);

const o="_prop1";
console.log(o),
console.log(o in obj),
console.log("o"in obj);