Read a for incremental loop
```ebnf
for ::= T_FOR '(' for_exprs ';' for_exprs ';' for_exprs ')' for_statement
for_statement ::= statement | ':' inner_statement_list T_ENDFOR ';'
for_exprs ::= expr? (',' expr)*
```
@see https://github.com/php/php-src/blob/master/Zend/zend_language_parser.y#L425
@return {For}
function() {
    const result = this.node("for");
    this.expect(this.tok.T_FOR) && this.next();
    let init = [];
    let test = [];
    let increment = [];
    let body = null;
    let shortForm = false;
    if (this.expect("(")) this.next();
    if (this.token !== ";") {
      init = this.read_list(this.read_expr, ",");
      if (this.expect(";")) this.next();
    } else {
      this.next();
    }
    if (this.token !== ";") {
      test = this.read_list(this.read_expr, ",");
      if (this.expect(";")) this.next();
    } else {
      this.next();
    }
    if (this.token !== ")") {
      increment = this.read_list(this.read_expr, ",");
      if (this.expect(")")) this.next();
    } else {
      this.next();
    }
    if (this.token === ":") {
      shortForm = true;
      body = this.read_short_form(this.tok.T_ENDFOR);
    } else {
      body = this.read_statement();
    }
    return result(init, test, increment, body, shortForm);
  }