Fix scalapb-runtime 0.11.17 errors

There were API changes from scalapb-runtime 0.9.7 causing the following
errors:

```txt
ERROR: .../test/src/main/scala/scalarules/test/extra_protobuf_generator/BUILD:3:14:
  scala @//test/src/main/scala/scalarules/test/extra_protobuf_generator:extra_protobuf_generator
  failed: (Exit 1): scalac failed: error executing Scalac command
  (from target //test/src/main/scala/scalarules/test/extra_protobuf_generator:extra_protobuf_generator)
  bazel-out/darwin_arm64-opt-exec-ST-a828a81199fe/bin/src/java/io/bazel/rulesscala/scalac/scalac
    ... (remaining 1 argument skipped)

test/src/main/scala/scalarules/test/extra_protobuf_generator/ExtraProtobufGenerator.scala:20:
  error: value nameSymbol is not a member of com.google.protobuf.Descriptors.Descriptor
      .add(s"final case object Custom${message.nameSymbol}{}")
                                               ^
test/src/main/scala/scalarules/test/extra_protobuf_generator/ExtraProtobufGenerator.scala:34:
  error: value fileDescriptorObjectName is not a member of com.google.protobuf.Descriptors.FileDescriptor
    b.setName(file.scalaDirectory + "/Custom" + file.fileDescriptorObjectName + ".scala")
                                                     ^
test/src/main/scala/scalarules/test/extra_protobuf_generator/ExtraProtobufGenerator.scala:66:
  error: value FileDescriptorPimp is not a member of scalapb.compiler.DescriptorImplicits
          import implicits.FileDescriptorPimp
                 ^
```

Since Scala 2.11 can't advance past scalapb-runtime 0.9.8, we use
`select_for_scala_version` to select the appropriate `ProtobufAdapter`
to maintain API compatibility.

Also, `import implicits.FileDescriptorPimp` turned out to be unnecessary
after all, even under Scala 2.11.

Author: mbland

test/src/main/scala/scalarules/test/extra_protobuf_generator/BUILD

@@ -1,8 +1,12 @@
 load("//scala:scala.bzl", "scala_library")
+load("//scala:scala_cross_version_select.bzl", "select_for_scala_version")
 
 scala_library(
     name = "extra_protobuf_generator",
-    srcs = ["ExtraProtobufGenerator.scala"],
+    srcs = select_for_scala_version(
+        any_2_11 = ["ProtobufAdapter_2_11.scala"],
+        since_2_12 = ["ProtobufAdapter.scala"],
+    ) + ["ExtraProtobufGenerator.scala"],
     visibility = ["//visibility:public"],
     deps = [
         "//scala_proto:scalapb_worker_deps",

test/src/main/scala/scalarules/test/extra_protobuf_generator/ExtraProtobufGenerator.scala

@@ -15,9 +15,11 @@ class CustomProtobufGenerator(
   import implicits._
   import ProtobufGenerator._
 
+  val protobufAdapter = new ProtobufAdapter(implicits)
+
   def printCustomMessage(printer: FunctionalPrinter, message: Descriptor): FunctionalPrinter = {
     printer
-      .add(s"final case object Custom${message.nameSymbol}{}")
+      .add(s"final case object Custom${protobufAdapter.nameSymbol(message)}{}")
   }
 
   override def generateSingleScalaFileForFileDescriptor(
@@ -31,7 +33,10 @@ class CustomProtobufGenerator(
         .result()
 
     val b = CodeGeneratorResponse.File.newBuilder()
-    b.setName(file.scalaDirectory + "/Custom" + file.fileDescriptorObjectName + ".scala")
+    b.setName(
+      file.scalaDirectory + "/Custom" +
+      protobufAdapter.fileDescriptorObjectName(file) + ".scala"
+    )
     b.setContent(code)
     List(b.build)
   }
@@ -79,7 +84,6 @@ object ExtraProtobufGenerator extends ProtocCodeGenerator {
           val generator = new CustomProtobufGenerator(params, implicits)
           val validator = new ProtoValidation(implicits)
           validator.validateFiles(filesByName.values.toSeq)
-          import implicits.FileDescriptorPimp
           request.getFileToGenerateList.asScala.foreach { name =>
             val file = filesByName(name)
             val responseFiles =

test/src/main/scala/scalarules/test/extra_protobuf_generator/ProtobufAdapter.scala

@@ -0,0 +1,13 @@
+package scalarules.test.extra_protobuf_generator
+
+import com.google.protobuf.Descriptors.{Descriptor, FileDescriptor}
+import scalapb.compiler.DescriptorImplicits
+
+class ProtobufAdapter(implicits: DescriptorImplicits) {
+    import implicits._
+
+    def nameSymbol(message: Descriptor): String = message.scalaType.nameSymbol
+
+    def fileDescriptorObjectName(file: FileDescriptor): String =
+        file.fileDescriptorObject.name
+}

test/src/main/scala/scalarules/test/extra_protobuf_generator/ProtobufAdapter_2_11.scala

@@ -0,0 +1,13 @@
+package scalarules.test.extra_protobuf_generator
+
+import com.google.protobuf.Descriptors.{Descriptor, FileDescriptor}
+import scalapb.compiler.DescriptorImplicits
+
+class ProtobufAdapter(implicits: DescriptorImplicits) {
+    import implicits._
+
+    def nameSymbol(message: Descriptor): String = message.nameSymbol
+
+    def fileDescriptorObjectName(file: FileDescriptor): String =
+        file.fileDescriptorObjectName
+}