[java] Removing the 'ELEMENT' key when serialising RemoteWebElement to Json

[pujagani]

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Description

Fixes #6393

Motivation and Context

The changes remove the legacy pointer 'ELEMENT' while serialising the RemoteWebElement to Json. This aligns with the Webdrive spec https://w3c.github.io/webdriver/#dfn-web-element-identifier
"The JSON serialization of an element is a JSON Object where the web element identifier key is mapped to the element’s web element reference."
"The web element identifier is the string constant "element-6066-11e4-a52e-4f735466cecf".

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.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[shs96c]

I'd rather leave this in until we figure out how to disentangle the JWP from the W3C protocols, while still offering people backwards compat through the server if they need it.

[titusfortner]

I don't think we'll get to this until/unless we completely revamp the Java code.