FORMS-10985: To validate theme for core components

[pranay-tippa]

Verifying the V2 Components themes in Preview.

Description

Added a test cases to validation of V2 Components themes in Preview using Visual testing by Cypress Image Diff.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes and the overall coverage did not decrease.
• All unit tests pass on CircleCi.
• I ran all tests locally and they pass.