Correctly apply comments for JSX

[silvenon]

When commenting a line using ⌘ + /, top-level JSX:

<Foo />

should turn into Markdown comments:

<!-- <Foo /> -->

and commenting content inside a JSX tag:

<Foo>
  <Bar />
</Foo>

should turn into JSX comments:

<Foo>
  {/* <Bar /> */}
</Foo>

[silvenon]

The latter case works now, but the first case still doesn't, and it's very tricky because it's JSX until it's commented, then it becomes treated as Markdown. 😓