Reads a switch statement
```ebnf
switch ::= T_SWITCH '(' expr ')' switch_case_list
```
@return {Switch}
@see http://php.net/manual/en/control-structures.switch.php
function() {
    const result = this.node("switch");
    this.expect(this.tok.T_SWITCH) && this.next();
    this.expect("(") && this.next();
    const test = this.read_expr();
    this.expect(")") && this.next();
    const shortForm = this.token === ":";
    const body = this.read_switch_case_list();
    return result(test, body, shortForm);
  }