Add product_available

Vendors already can use these targets on /vendor. This change makes them
available to /product as well.

More about product partitions:
https://source.android.com/docs/core/architecture/partitions/product-partitions

Bug: 336989719
Test: mm
Change-Id: Ieb94958ad2e3a909dac03a2e7ee0a29168ac9acf
diff --git a/Android.bp b/Android.bp
index e6ca9e0..6918e80 100644
--- a/Android.bp
+++ b/Android.bp
@@ -15,6 +15,7 @@
     name: "libabsl",
     host_supported: true,
     vendor_available: true,
+    product_available: true,
     srcs: [
         "absl/**/*.cc",
     ],