Fix 'Container is falsy' bug due to Babel upgrade

[benjie]

Description

What we were doing worked, but was broken by Babel's latest patch release; thanks to @nckswt for tracking it down in benjie/ouch-my-finger#16 (comment) and narrowing down that it works fine with @babel/[email protected] but surfaces the error in @babel/[email protected]

This PR reworks our solution based on the approach outlined in babel/babel#15544 (comment)

Performance impact

Unknown.

Security impact

None known.

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[changeset-bot]

🦋 Changeset detected

Latest commit: c69b2fd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
eslint-plugin-graphile-export	Patch
graphile-export	Patch
postgraphile	Patch
pgl	Patch
graphile	Patch

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