fix: retain all fields during ServiceOptions.tobuilder

[burkedavison]

See #2821

This PR originally created to ensure headerProvider is correctly copied, but expanded to ensure all fields are used in equals and hashCode comparisons for the associated copy tests.

[sonarqubecloud[bot]]

Quality Gate passed for 'gapic-generator-java-root'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
75.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

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 SonarCloud

[burkedavison]

Downstream checks failing on serialization tests.