Confusing error message when closing curly brace is missing in a template literal string

[BJ Burg]

STEPS TO REPRODUCE:

Here's a test case that runs in the JSC shell:

>>> var foo = 123; var bar = `aaa bbb '${typeof foo'.`; 42;
Unexpected EOF:1


NOTES:

A useful error message occurs in this use case:

>>> var foo = 123; var bar = `aaa bbb '${typeof foo  ccc'.`; 42;
Unexpected identifier 'ccc'. Expected a closing '}' following an expression in template literal.:1

[Joseph Pecoraro]

> >>> var foo = 123; var bar = `aaa bbb '${typeof foo'.`; 42;

There are a couple interesting things here.

  (1) The error comes from attempting to start parsing the nested template string:

      This is valid: ` ... ${ ... `nested` }`
      In the above, the nested template is `; 42;<EOF>`.

  (2) We could have errored out sooner, in cases like:

        foo.' (tokenizes a string)
        foo.` (tokenizes a template string)