chore: Add load()s for the Bazel builtin java rules

[hvadehra]

load() statements are being added to prepare for moving the rules out of Bazel and into rules_java

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Fixes #2683

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[blakeli0]

Thanks for the contribution @hvadehra! Do you mind creating an issue for this PR?
Just curious, why do we need this change? I guess java_test is going to be moved out of native Bazel? Also how did you find out we are using java_test, by searching all Google repos?

[hvadehra]

Created #2683

Also how did you find out we are using java_test?

I was migrating changes internally, and cl/622846271 got submitted. Unfortunately, my reviewer did not catch that the SoT was github, and changes got overwritten in the next import a few days ago.

[blakeli0]

/gcbrun

[sonarqubecloud]

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

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

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