[decorators] Set method names at compile time instead of at runtime

[nicolo-ribaudo]

Q	A
Fixed Issues?	Fixes #9234
Patch: Bug Fix?	yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

In gh-8743 I used Object.defineProperty in the decorators helper
to set the correct methods name: it was needed because methods were
renamed to value. Apparently some browsers set Function#name as
non-configurable: gh-9234, so it throws.

This commit removes that fix from the helper and changes the
transform so that it gives the correct name at compile time. It
doesn't work with computed keys, but it should be ok because we
already don't handle method names in classes and object methods.

Output for methods, classes and decorated classes

Objects:

In:

var key = "k";
var obj = {
  fn() {},
  [key]() {}
}

Out:

var key = "k";

var obj = _defineProperty({
  fn: function fn() {}
}, key, function () {});

Test:

obj.fn.name; // "fn"
obj.k.name; // ""

Classes:

In:

var key = "k";
class Cl {
  fn() {}
  [key]() {}
}

Out:

var key = "k";

var Cl =
/*#__PURE__*/
function () {
  function Cl() {
    _classCallCheck(this, Cl);
  }

  _createClass(Cl, [{
    key: "fn",
    value: function fn() {}
  }, {
    key: key,
    value: function () {}
  }]);

  return Cl;
}();

Test:

new Cl().fn.name; // "fn"
new Cl().k.name; // "value"

Decorated classes:

In:

var key = "k";

@(_ => _)
class DecCl {
  fn() {}
  [key]() {}
}

Out:

var key = "k";

let DecCl = _decorate([_ => _], function (_initialize) {
  class DecCl {
    constructor() {
      _initialize(this);
    }

  }

  return {
    F: DecCl,
    d: [{
      kind: "method",
      key: "fn",
      value: function fn() {}
    }, {
      kind: "method",
      key: key,
      value: function () {}
    }]
  };
});

Test:

new Cl().fn.name; // "fn"
new Cl().k.name; // "value"

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9662/