WIP! Implement optional chaining and import.meta

[KFlash]

This is still a WIP, and can't be finished before we know the ESTree specs for it.

For now this implementation is based on this ESTree discussion and how optional chaining is done in V8, SM and Webkit.

Import.meta added here to avoid conflicts later on.

[KFlash]

@aladdin-add chained: 0 | 1 = 0 is temporary because we don't know the ESTree specs yet. Added to be in line with the Babel parser :) When you figure it out with ESTree this has to either 1) be removed or 2) moved up to be in sync withinGroup and = 0 removed so every call to parseMemberOrUpdateExpression has to have a 0 as func arg.

Example: parseMemberOrUpdateExpression(parser, context, /* inGroup */ 0, /* chained */ 0, start, line, column)

If you figure out that the OptionalMemberExpression shouldn't be there, well just remove it and use the original one and update estree.ts as well.

[KFlash]

@aladdin-add After studying the specs I think Babel's implementation is wrong and not how it will be.

My current changes are more in line with what suggested in one of the ESTree discussion from 2017.

I will push this changes soon, but here is an example.

Note the new OptionalChain AST node

You parse this: a.b?.c

Outputs:

{
          "body": [
            {
              "expression": {
                "expr": {
                  "computed": false
                  "object": {
                    "computed": false
                    "object": {
                      "name": "a"
                      "type": "Identifier"
                    }
                    "property": {
                      "name": "b"
                      "type": "Identifier"
                    }
                    "type": "MemberExpression"
                  }
                  "optional": true
                  "property": {
                    "name": "c"
                    "type": "Identifier"
                  }
                  "type": "MemberExpression"
                }
                "type": "OptionalChain"
              }
              "type": "ExpressionStatement"
            }
          ]
          "sourceType": "script"
          "type": "Program"
        }

[KFlash]

@aladdin-add and others. I enabled optional chaining and other new Stage 3 proposals available in the REPL so this PR can be tested live there.

REPL: https://meriyah.github.io/meriyah/

Here is the benchmark results with this PR implemented. It looks like I got a performance regression :(

@axefrog Ideas what can have caused this regression?

[KFlash]

@aladdin-add Fixed the performance regression. There was a regression while parsing larger libraries. Hard to see for people that doesn't know this code :)

Here is the new benchmark results. And we are good to go 👍

[KFlash]

@aladdin-add Added import.meta into this PR to avoid conflicts. Any progress with the ESTree specs?