Handle schema errors

[sobolk]

Problem

Invalid and empty schema errors indicate invalid inputs. I.e. user error.

Changes

Map these errors.

Validation

Added test.

Checklist

• [ ] If this PR includes a functional change to the runtime behavior of the code, I have added or updated automated test coverage for this change.
• [ ] If this PR requires a change to the Project Architecture README, I have included that update in this PR.
• [ ] If this PR requires a docs update, I have linked to that docs PR above.
• [ ] If this PR modifies E2E tests, makes changes to resource provisioning, or makes SDK calls, I have run the PR checks with the run-e2e label set.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: c21b27dbba1ad2584e2b621ef4c437bbb98252e3

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

This PR includes changesets to release 1 package

| Name | Type | | ----------------------------- | ----- | | @aws-amplify/schema-generator | Patch |

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