fix(babel-preset-gatsby): Ensure the spread operator works correctly on Sets

[circlingthesun]

Description

The current @babel/preset-env config defaults to loose transforms which results in incorrect semantics when the spread operator is applied to a Set.

Executing

[...new Set([1, 2, 2, 3])]

results in

[Set(1, 2, 3)]

when

[1, 2, 3]

is expected.

This PR ensures that the expected result is obtained by configuring @babel/plugin-transform-spread to follow ECMAScript semantics.

Related Issues

Fixes #14848

[wardpeet]

Thank you for opening this PR! This is a great change. We can't just flip the switch on the @babel/preset-env so I think this is a great way to sidestep this behaviour.

Thank you for your patience!

[gatsbot]

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[wardpeet]

Fixed in babel-preset-gatsby@0.2.3