[java][bidi]: implement getClientWindows method

[navin772]

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Description

Implemented getClientWindows method in java for BiDi and added the test.

BiDi spec - https://w3c.github.io/webdriver-bidi/#command-browser-getClientWindows

Currently the PR is a draft as the above method is not released for stable, tested out with firefox nightly and chrome canary.

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 read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.