Move api text files to android.txt/xml.

Mistake in aosp/661881 which migrated existing text files. Name the api file
for android.jar android.txt instead of N.txt, as described in the DD:
go/android-uses-libraries.

Also fix the Android.bp references.

Moves generated by:
$ for f in */*/api/*.xml; do mv "$f" "$(dirname $f)/android.xml"; done
$ for f in */*/api/*.txt; do mv "$f" "$(dirname $f)/android.txt"; done

Bug: 77525052
Test: These files are currently unused, but tested via make in follow-up CLs.
Change-Id: Ia4c88c0ce76400b5ede121d5b00b394d1fc4db5c
diff --git a/Android.bp b/Android.bp
index e691e5c..f78262f 100644
--- a/Android.bp
+++ b/Android.bp
@@ -3,8 +3,8 @@
 filegroup {
     name: "api-version-xml",
     srcs: [
-        "*/*/api/*.txt",
-        "*/*/xml/*.txt",
+        "*/public/api/android.txt",
+        "*/public/api/android.xml",
         "api/*.xml",
         "api/*.txt",
     ],