Change DefaultHttpDataSourceTest to an instrumentation test

The Robolectric implementation of HttpURLConnection forwards to the JRE
implementation [1], which behaves differently to the Android one
available on devices and emulators. For these tests to be a realistic
test of the HTTP stack used in real playbacks we can't use Robolectric.

Similar to https://github.com/google/ExoPlayer/commit/df0e89c1678ff0dda00bb187be05b8198bd31567

[1] https://github.com/robolectric/robolectric/issues/6769#issuecomment-943556156

PiperOrigin-RevId: 416013662

library/datasource/build.gradle

@@ -42,6 +42,7 @@ dependencies {
     androidTestImplementation 'androidx.test:runner:' + androidxTestRunnerVersion
     androidTestImplementation 'com.linkedin.dexmaker:dexmaker:' + dexmakerVersion
     androidTestImplementation 'com.linkedin.dexmaker:dexmaker-mockito:' + dexmakerVersion
+    androidTestImplementation 'com.squareup.okhttp3:mockwebserver:' + okhttpVersion
     androidTestImplementation(project(modulePrefix + 'testutils')) {
         exclude module: modulePrefix.substring(1) + 'library-core'
     }