[Enhancement] Use Java toolchain for gradle

[CXwudi]

Would you consider replacing:

java {
  sourceCompatibility = JavaVersion.VERSION_21
}

with:

java {
  toolchain {
    languageVersion.set(JavaLanguageVersion.of(21))
  }
}

Since the java toolchain is what Gradle preferred in its guide

Also, toolchain has the benefit of automatically download the declared Java distribution if one is missing in the host machine

[wilkinsona]

Duplicates #1227.