feat(fsx): throw ValidationErrors instead of untyped Errors

[badmintoncryer]

Issue # (if applicable)

Relates to #32569

Reason for this change

Untyped Errors are not recommended.

Description of changes

Change Error to ValidationError / UnscopedValidationError

Describe any new or updated permissions being added

None

Description of how you validated changes

Existing tests. Exemptions granted as this is a refactor of existing code.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

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

[aws-cdk-automation]

The pull request linter fails with the following errors:

❌ Features must contain a change to a README file.
❌ Features must contain a change to a test file.
❌ Features must contain a change to an integration test file and the resulting snapshot.

If you believe this pull request should receive an exemption, please comment and provide a justification. A comment requesting an exemption should contain the text Exemption Request. Additionally, if clarification is needed, add Clarification Request to a comment.

✅ A exemption request has been requested. Please wait for a maintainer's review.

[badmintoncryer]

Exemption Request: This PR did only refactoring.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.98%. Comparing base (74cbe27) to head (14d6345).
Report is 30 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #34120   +/-   ##
=======================================
  Coverage   83.98%   83.98%           
=======================================
  Files         120      120           
  Lines        6976     6976           
  Branches     1178     1178           
=======================================
  Hits         5859     5859           
  Misses       1005     1005           
  Partials      112      112           

Flag	Coverage Δ
suite.unit	83.98% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	83.98% <ø> (ø)

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 14d6345
• Result: SUCCEEDED
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