Braced object literal shorthand

[edemaine]

Implements the following braced object literal shorthand (the first part of #238):

• {props.name} → {name: props.name} (and name={props.name} in JSX context)
• {computed()} → {computed: computed()}
• {x.y?.z?()} → {z: x.y?.z?()}

This PR newly forbids methods with no body. However, method(){} specifies an empty body.

Some potentially confusing behavior is that { console.log('hello', name) } is now potentially an object literal (or a block), namely { log: console.log('hello', name) }. This broke one test case that used a weird mix of for loop notation: no parens around the condition, but braces around the block:

for [i, j] of x {
  console.log(i)
}

This is still broken: doesn't parse, because for loop has no body. Proposal is that for loops should use parens and braces, or neither.

[STRd6]

I've been starting to replace the loose leading __ with ( Samedent / _ )?. The __ in between open and close in fine.

Not something that needs to be done in this PR just something I wanted to share as we move towards more strict/robust indenting.