Add a way to create snapshot repository directory

Add a way to build all the androidx libraries where every project
version is replaced with A.B.C-SNAPSHOT.

For these snapshot builds, maven plugin tasks will put their results
to dist/ directory that will make them accessible to users of
ci.android.com

This CL also introduces Publish enum that allows library to show up
in snapshots but not be released.

This will allow developers to point their local build.gradle files to
test out snapshots of our libraries by adding something like:
repositories {
  maven {
    url "https://ci.android.com/builds/submitted/5610982/androidx/latest/view/repository"
  }
}

Test: SNAPSHOT=true ./gradlew createArchive -> creates a repository directory in out/dist
Change-Id: I3e4ef04b59d2e5114f8aeaf6aca5bb0c931c1397
diff --git a/animation/build.gradle b/animation/build.gradle
index f0a633e..b965764 100644
--- a/animation/build.gradle
+++ b/animation/build.gradle
@@ -17,6 +17,7 @@
 import static androidx.build.dependencies.DependenciesKt.*
 import androidx.build.LibraryGroups
 import androidx.build.LibraryVersions
+import androidx.build.Publish
 
 plugins {
     id("AndroidXPlugin")
@@ -34,7 +35,7 @@
 
 androidx {
     name = "Android Support Animation"
-    publish = false
+    publish = Publish.NONE
     mavenVersion = LibraryVersions.ANIMATION
     mavenGroup = LibraryGroups.ANIMATION
     inceptionYear = "2018"