Use AutoService as a proper annotation processor.

I was going to say that this also paves the way for including the annotation as a non-optional dependency, should we wish to follow our Guava precedent for annotations:
- google/guava#2824
- google/guava#2721

But I see that it's retention=SOURCE anyway, so there isn't much reason to do that -- except maybe consistency with other annotation packages someday. (Maybe it's still a negative then, as it might still let people rely on our transitive dependency?)

I think the relationship of all this to Java 11 was that I might have to set an Automatic-Module-Name on AutoService, and it makes more sense to set it after we've done the processor-vs.-annotation artifact split. Once I was upgrading, it made sense to set up the annotation processor the Right Away, now that we're using a version in which that works. (Or maybe it always worked but now it's nice that it gets the processor off the classpath?) Or maybe there was some other reason for the change to the annotation-processor setup; once again, I forget. It looks like it might have been that AutoService stops running when I switch how we run Error Prone. Hopefully this was the solution :) But it's probably a good idea in any case.

This CL is basically following the "alternatively" instructions in https://github.com/google/auto/blob/master/value/userguide/index.md#in-pomxml

...even though the AutoService instructions haven't been similarly updated yet: https://github.com/google/auto/tree/master/service#download

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=272720556

jimfs/pom.xml

@@ -52,7 +52,7 @@
     <!-- Compile-time dependencies -->
     <dependency>
       <groupId>com.google.auto.service</groupId>
-      <artifactId>auto-service</artifactId>
+      <artifactId>auto-service-annotations</artifactId>
       <optional>true</optional>
     </dependency>
     <dependency>

pom.xml

@@ -86,6 +86,7 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <auto-service.version>1.0-rc6</auto-service.version>
     <java.version>1.7</java.version>
     <guava.version>27.0.1-android</guava.version>
   </properties>
@@ -109,8 +110,8 @@
       <!-- Compile-time dependencies -->
       <dependency>
         <groupId>com.google.auto.service</groupId>
-        <artifactId>auto-service</artifactId>
-        <version>1.0-rc3</version>
+        <artifactId>auto-service-annotations</artifactId>
+        <version>${auto-service.version}</version>
       </dependency>
       <dependency>
         <groupId>com.google.code.findbugs</groupId>
@@ -190,6 +191,11 @@
               <artifactId>guava-beta-checker</artifactId>
               <version>1.0</version>
             </path>
+            <path>
+              <groupId>com.google.auto.service</groupId>
+              <artifactId>auto-service</artifactId>
+              <version>${auto-service.version}</version>
+            </path>
           </annotationProcessorPaths>
         </configuration>
         <executions>