Upgrade Gradle to version 7.3.3 (#1822)

* Upgrade to Gradle 7.3.3

Necessary changes include:
- Rename configurations created by the `java` plugin.
- Upgrade the `protobuf-gradle-plugin` to avoid the "Configuration with
  name 'compile' not found" error.
- Remove the deprecated `kotlin.parallel.tasks.in.project` property, which
  got replaced by the Gradle parallel project execution option.
- Stop using the deprecated `maven` plugin in favor of only the
  `maven-publish` plugin [1].
- Remove the deprecated / inactive `GRADLE_METADATA` feature preview
  flag [2] [3].
- For yet unclear reasons the JUnit imports in the HOCON tests needed to
  be made explicit to avoid compile errors.

[1]: https://docs.gradle.org/4.8/release-notes.html
[2]: https://github.com/gradle/gradle/pull/16118
[3]: https://kotlinlang.org/docs/migrating-multiplatform-project-to-14.html#simplify-your-build-configuration

* Gradle: Remove an unused import

* Gradle: Use single quotes where no variable interpolation is required

* Gradle: Use the compact string notation to declare dependencies

This creates consistency with the majority of declarations.

1 files changed, 0 insertions, 2 deletions

diff --git a/integration-test/settings.gradle b/integration-test/settings.gradle
index 9410dc0c..2360ae47 100644
--- a/integration-test/settings.gradle
+++ b/integration-test/settings.gradle
@@ -22,5 +22,3 @@ pluginManagement {
 }
 
 rootProject.name = 'kotlinx-serialization-integration-test'
-
-enableFeaturePreview('GRADLE_METADATA')