Gracefully handle template literal properties in the parser

``` TypeScript
var x = {
a: "Hello"
`b`: 123
}
```

Right now, the parser encounters the template string, decides it should bail out of object literal parsing, and we more or less recover thinking we have something like the following:

``` TypeScript
var x = ({ a: "Hello" } `b`) : 123 }
```

So we'll report an error on what we think is:

``` TypeScript
{ a: "Hello" } `b`
```
- On the syntactic layer under ES5 mode, we'll say tagged templates are not supported unless in ES6.
- On the semantic layer, we'll say `{ a: "Hello" }` is not invokable.

Start at the parser's object-literal handling and reproduce the shown template-literal property case under ES5 and ES6 modes. Trace how the parser recovers at the template string and compare the resulting syntactic and semantic diagnostics. Done means this malformed or unsupported construct receives appropriate diagnostics without being misread as a tagged call.

Written by the indexing model from the issue text.