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

java/sdk_library_test.go

@@ -851,6 +851,13 @@ func TestJavaSdkLibraryDist(t *testing.T) {
 			srcs: ["foo.java"],
 		}
 
+		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,
@@ -884,6 +891,11 @@ func TestJavaSdkLibraryDist(t *testing.T) {
 			distDir:  "apistubs/android/public",
 			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",