Enable unused Typescript enums to be removed by minifiers

[mischnic]

Typescript enums should be transpiled such that they can be removed by minifiers if not used.

So

enum Test {
    Key = 1
}

currently becomes

var Test;
(function(Test) {
    Test[Test["Key"] = 1] = "Key";
})(Test || (Test = {}));

but should be

var Test = /* @__PURE__ */ ((x) => {
  x[x["Key"] = 1] = "Key";
  return x;
})(Test || {});

Context

Related issues:
Babel: babel/babel#9268
TSC: microsoft/TypeScript#27604
Terser: terser/terser#1177
Esbuild does this already: terser/terser#1177 (comment)

[swc-bot]

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