Ensure expressions wrapped in parens

[overlookmotel]

Fix for #12055.

The fix itself is very simple. I've added tests for the original bug and also some other weird cases which were previously producing incorrect output.

I am assuming that existing behavior for standalone expressions is correct.

i.e. generate( t.objectExpression([]) ).code should produce {} not ({}). Certainly that's what I want it to be!

One case produces excess parentheses:

t.arrowFunctionExpression(
  [],
  t.sequenceExpression([
    t.objectExpression([]),
    t.numericLiteral(1)]
  )
)

This generates () => (({}), 1). I couldn't see a way to avoid this without introducing excess complexity for a pretty uncommon case.

Please shout if you want any changes.

Q	A
Fixed Issues?	Fixes #12055
Patch: Bug Fix?	Y
Major: Breaking Change?	N
Minor: New Feature?	N
Tests Added + Pass?	Yes
Documentation PR Link	n/a
Any Dependency Changes?	N
License	MIT

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[JLHwung]

Thanks.

[existentialism]

@overlookmotel thanks!

[overlookmotel]

@existentialism No worries. Thanks for getting it merged swiftly.