fix: Validate js-sdk-file input for Gradle 8 compatibility

[Mansi-mParticle]

Background

• This PR updates the js-sdk-file handling to be compatible with Gradle 8’s stricter
  file and configuration validation.

What Has Changed

• Validate that the js-sdk-file property exists and points to a valid file.

Screenshots/Video

• {Include any screenshots or video demonstrating the new feature or fix, if applicable}

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have tested this locally.

Additional Notes

• {Any additional information or context relevant to this PR}

Reference Issue (For employees only. Ignore if you are an outside contributor)

• Closes https://go/j/[ticket-number]

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud