Make SDC library widget tests use Robolectric

[jingtang10]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes #1330

Description
Make SDC library widget tests use Robolectric

Alternative(s) considered
NA

Type
Testing

Screenshots (if applicable)
NA

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[omarismail94]

Removing code is the best type of code!

[codecov]

Codecov Report

Merging #1332 (d43c3ad) into master (13aa710) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1332   +/-   ##
=========================================
  Coverage     84.57%   84.57%           
  Complexity      687      687           
=========================================
  Files           148      148           
  Lines         10701    10701           
  Branches        832      832           
=========================================
  Hits           9050     9050           
  Misses         1237     1237           
  Partials        414      414           

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