Add Selenium Support package to java_repositories()

[ptmphuong]

This package is needed when a user wants to use the Java WebTest API with Selenium Wait to interact with G_testrunner.

Usage example:

import com.google.testing.web.WebTest;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.support.ui.FluentWait;

public class TestDriver {
  private WebDriver driver;
  private String testURL;

  public WebtestDriver(String testURL) {
    this.driver = new WebTest().newWebDriverSession();
    this.testURL = testURL;
  }

  public void run() {
    driver.get(this.testURL);

    new FluentWait<>((JavascriptExecutor) driver)
        .pollingEvery(Duration.ofMillis(POLL_INTERVAL))
        .withTimeout(Duration.ofSeconds(TEST_TIMEOUT))
        .until(executor ->
                (boolean) executor.executeScript("return window.top.G_testRunner.isFinished()")));
  }
}

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[gkdn]

@mtrea I'm not sure what is the prefer process. Would you prefer this PR or a CL for this?

[mtrea]

GitHub is our preferred source-of-truth, so this is correct, thanks!

[mtrea]

You can upstream this internally, just go ahead and cite this pull request in the CL description.