Test exporting schemas, fix schema exporting

[benjie]

Description

Now schemas cannot be exported unless the functions within them don't reference globals, we can test that our standard schemas are exportable in order to catch bugs where we've failed to add EXPORTABLE in various places.

This fixes a few of these places.

Performance impact

The tests run a lot slower now!

Security impact

Improvement: exports more likely to be valid.

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: 3e2b5b4

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

This PR includes changesets to release 16 packages

Name	Type
tamedevil	Patch
graphile-build-pg	Patch
graphile-build	Patch
postgraphile	Patch
graphile-export	Patch
grafast	Patch
ruru-components	Patch
graphile-utils	Patch
pgl	Patch
graphile	Patch
@dataplan/pg	Patch
@localrepo/grafast-bench	Patch
@dataplan/json	Patch
@grafserv/persisted	Patch
grafserv	Patch
@localrepo/grafast-website	Patch

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