fix(eslint-parser): merge input estree options

[JLHwung]

Q	A
Fixed Issues?	@babel/eslint-parser users should be able to opt-in to the classFeatures: boolean
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

In #12867 we move estree class features behind a classFeatures: boolean option. However it is impossible to be allowed in @babel/eslint-parser because Babel parser does not merge plugin options. In this PR we merge user supplied estree options to the builtin estree options defaults.

After this PR is shipped, you can specify classFeatures to enable estree class features implementation in .eslintrc.js:

module.exports = {
  parser: "@babel/eslint-parser",
  parserOptions: {
    requireConfigFile: false,
    babelOptions: {
      parserOpts: {
        plugins: [
          ["estree", { classFeatures: true }],
          "classPrivateProperties",
          "classProperties",
        ],
      },
    },
  },
};

cc @fisker

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/42451/

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[nicolo-ribaudo]

Looks good!

I'd label this as a [Bug fix], since it's an observable change in the behavior.

[fisker]

Great , thank you .