Export monolithic hidden API files from platform_bootclasspath

Makes the monolithic hidden API files accessible from the
platform_bootclasspath so they can be output to the dist build target
and used by other modules, e.g. by doing something like this:
  java_resources: [
    ":platform-bootclasspath{hiddenapi-flags.csv}",
  ],

It makes the paths relative to the out/soong/hiddenapi directory rather
than the out/soong directory to make them easier to use in the
java_resources property without changing the structure of the APK.
Without that attempting to use them in a java_resources property will
result in them being copied to a hiddenapi/ within the APK instead of
being used at the top level as existing APKs like
CtsHiddenApiBlocklistTestApiTestCases expect.

Bug: 177892522
Test: m nothing
Change-Id: I829412fc7d25411e0c2e0713d0d219a18f4af2ee

java/platform_bootclasspath_test.go

@@ -131,3 +131,44 @@ func TestPlatformBootclasspath(t *testing.T) {
 		})
 	})
 }
+
+func TestPlatformBootclasspath_Dist(t *testing.T) {
+	result := android.GroupFixturePreparers(
+		prepareForTestWithPlatformBootclasspath,
+		dexpreopt.FixtureSetBootJars("platform:foo", "platform:bar"),
+		android.PrepareForTestWithAndroidMk,
+		android.FixtureWithRootAndroidBp(`
+			platform_bootclasspath {
+				name: "platform-bootclasspath",
+				dists: [
+					{
+						targets: ["droidcore"],
+						tag: "hiddenapi-flags.csv",
+					},
+				],
+			}
+
+			java_library {
+				name: "bar",
+				srcs: ["a.java"],
+				system_modules: "none",
+				sdk_version: "none",
+				compile_dex: true,
+			}
+
+			java_library {
+				name: "foo",
+				srcs: ["a.java"],
+				system_modules: "none",
+				sdk_version: "none",
+				compile_dex: true,
+			}
+		`),
+	).RunTest(t)
+
+	platformBootclasspath := result.Module("platform-bootclasspath", "android_common").(*platformBootclasspathModule)
+	entries := android.AndroidMkEntriesForTest(t, result.TestContext, platformBootclasspath)
+	goals := entries[0].GetDistForGoals(platformBootclasspath)
+	android.AssertStringEquals(t, "platform dist goals phony", ".PHONY: droidcore\n", goals[0])
+	android.AssertStringEquals(t, "platform dist goals call", "$(call dist-for-goals,droidcore,out/soong/hiddenapi/hiddenapi-flags.csv:hiddenapi-flags.csv)\n", android.StringRelativeToTop(result.Config, goals[1]))
+}