Support for ES2020 Optional chaining

[ljqx]

This PR fixes #2023.

Several changes are made:

• The new nodes (properties) defined in ESTree spec, including ChainExpression, ChainElement (optional property for MemberExpression and CallExpression)
• Scanner logic for ?., which cannot follow a digit.
• Parser logic for ?.
  • in CallExpression, computed MemberExpression, or static MemberExpression
  • Optional chaining cannot be assignment target
  • Optional chaining cannot work with template string (Note the error message is different for direct chaining a?.'b' with template string or indirect a?.b'c', here apostrophe is used as backtick)
  • ChainExpression is only inserted when in the chain there is optional chaining
• Tests are updated
  • Unit tests fixtures and integration tests fixtures need to be updated to add the new optional: false property for MemberExpression and CallExpression
  • Test 262 whitelist is updated (Note test/language/expressions/optional-chaining/call-expression-super-no-base.js is whitelisted because of super() in non derived class #2000
  • api tests is updated to include the new node type

[JingleH]

When can this be merged? It would be really helpful! Thanks!

[lahma]

@ljqx has done great work with the new features, kudos! Let's give @ariya some time to check it, I know that there can be a lot going on, like work and family.

[6uliver]

When could you review and merge this PR since it's a blocking issue for other packages which are using esprima like this one: i18next/i18next-scanner#205

Can I help you somehow to speed up the process?

[jogibear9988]

@ljqx @ariya any news to this, when this could be merged?

[johnjbarton]

We get a lot of complaints now about esprima failing on optional chaining.

[ljqx]

Will be reviewed in this weekend, thanks @ariya !

[ariya]

Excellent work 🥇