Parser: fix Octal escape such as \75 to be treated as an Octal number, not Decimal

/\75/

Should parse into:

{
  "type": "Char",
  "value": "\\75",
  "kind": "oct",
  "symbol": "=",
}

And not to:

{
  "type": "Char",
  "value": "\\75",
  "kind": "decimal",
  "symbol": "K",
}

See LegacyOctalEscapeSequence in Annex B: http://www.ecma-international.org/ecma-262/7.0/#sec-additional-syntax-string-literals

[DmitrySoshnikov]

Yeah, with u flag it’s an invalid encoding. I’m not sure whether regexp-tree needs to actively and fully support Annex B (after all it’s a depurated legacy stuff). Probably only for interpreter module, which still should interpret /\75/.test('='); as true. Not sure if it’s even essential for the parser now. But for the parser, yes, it goes to LegacyOctalEscapeSequence.

[DmitrySoshnikov]

@qfox, ah, autocorrect for “depurated”, but that’s right 😃 Yeah, I think we still need to fix and treat \75 and other as Octal, and match = in the interpreter.