Use Launcher aconfig flag in Resource file.

Use BaseIconRoot as an example. Also add bpfmt file formatting.

Bug: 393609690
Test: Verified compilation worked well and font actually built
successfully in both gradle and make.
Flag: com.android.launcher3.google_sans_flex_font

Change-Id: I2200d13a8d57e5d046a35226f08a751add937ca7
diff --git a/Android.bp b/Android.bp
index a4a058f..dccbf2f 100644
--- a/Android.bp
+++ b/Android.bp
@@ -408,6 +408,9 @@
     lint: {
         baseline_filename: "lint-baseline.xml",
     },
+    flags_packages: [
+        "com_android_launcher3_flags",
+    ],
 }
 
 //