fix(7410): Support JSX Element as JSX Attribute Value

[a-tarasyuk]

Fixes #7410

JSXAttributeValue:
    " JSXDoubleStringCharactersopt "
    ' JSXSingleStringCharactersopt '
    { AssignmentExpression }
    JSXElement
    JSXFragment

• JSX spec
• wrap JSX element attributes in expression babel/babel#6006 / Example

[RyanCavanaugh]

Waiting for final confirmation on facebook/jsx#53 before merging/closing.

[RyanCavanaugh]

@raghavthind2005 bulk-"approving" changes like what you're doing here is a little spammy; please refrain from doing this

[sandersn]

@RyanCavanaugh are we still waiting on confirmation from facebook/jsx to merge this?

[RyanCavanaugh]

Maybe let's just merge it. If the JSX spec changes, we'll have the same mess to clean up as Babel, which is fine