Support dist_group property instead of owner for setting sdk dist subdirectory

Reusing the owner property is confusing, especially when the property is
required on every java_sdk_library module.  Create a new dist_group property
to use instead.

Bug: 186723288
Test: TestJavaSdkLibraryDist
Change-Id: I9e62c703a95d6b63cafa60bffb1b37ba85388593
diff --git a/java/sdk_library_test.go b/java/sdk_library_test.go
index 84b5a24..0fe6e72 100644
--- a/java/sdk_library_test.go
+++ b/java/sdk_library_test.go
@@ -852,6 +852,13 @@
 		}
 
 		java_sdk_library {
+			name: "sdklib_group_foo",
+			unsafe_ignore_missing_latest_api: true,
+			srcs: ["foo.java"],
+			dist_group: "foo",
+		}
+
+		java_sdk_library {
 			name: "sdklib_owner_foo",
 			unsafe_ignore_missing_latest_api: true,
 			srcs: ["foo.java"],
@@ -885,6 +892,11 @@
 			distStem: "sdklib_no_owner.jar",
 		},
 		{
+			module:   "sdklib_group_foo",
+			distDir:  "apistubs/foo/public",
+			distStem: "sdklib_group_foo.jar",
+		},
+		{
 			module:   "sdklib_owner_foo",
 			distDir:  "apistubs/foo/public",
 			distStem: "sdklib_owner_foo.jar",