refactor: Convert Maven-based datasources to class (#14188)

lib/datasource/api.ts

lib/datasource/clojure/__snapshots__/index.spec.ts.snap

lib/datasource/clojure/index.ts

lib/datasource/maven/index.spec.ts

lib/datasource/maven/index.ts

lib/datasource/maven/util.ts

lib/datasource/metadata.spec.ts

lib/datasource/sbt-package/index.spec.ts

lib/datasource/sbt-package/index.ts

lib/datasource/sbt-package/util.ts

lib/datasource/sbt-plugin/index.spec.ts

lib/datasource/sbt-plugin/index.ts

lib/manager/gradle/deep/gradle-updates-report.ts

lib/manager/gradle/deep/index.ts

lib/manager/gradle/index.ts

lib/manager/gradle/shallow/extract.ts

lib/manager/maven/extract.ts

lib/manager/maven/index.ts

lib/manager/sbt/extract.ts

lib/manager/sbt/index.ts