Fix1736

[IwanKaramazow]

Fixes #1736

This PR adds printing of braces around JSX as JSX-arguments:

<Description term={<Text text="Age" />}> ... </Description>;
<Foo bar={<Baz />} />

Error messages for ambiguous cases are also provided:

[strega-nil]

This seems unfortunate. Could we make it context dependent instead?

[jordwalke]

Great! So, if we convert some code from OCaml to Reason that uses />>, how is it printed? I think we need a way to express the />>identifier with some test cases showing that it is possible. Perhaps you could have a special tokenizer rule for \/>> which parses into />>?

[IwanKaramazow]

Per discussion with @chenglou, braces are printed around JSX as jsx-arguments:

<Description term={<Text text="Age" />}> ... </Description>;
<Foo bar={<Baz />} />

The infix operators are preserved this way, also added tests, and it's a bit more familiar for JS-developers.
Error messages for ambiguous cases are also provided:

[thangngoc89]

Why don’t we use normal () braces? Those curly braces look ugly

[chenglou]

@thangngoc89 mostly for familiarity with existing JSX, and to reduce the amount of parentheses.

[jordwalke]

To reduce the number of parens, we could print them as { } in any other JSX cases that require parens. It needn't block this diff, but one more "Good First Task" if anyone's interested.

[jordwalke]

Probably worth pulling out JSX logic into its own module in the future.

[jordwalke]

Thank you again! Merged.