Tidy up API build variables

1) Delete unused Docs.mk.

This removes the last reference to non_openjdk_java_files.bp and
openjdk_java_files.bp filegroups from .mk files.
This means that export_to_make_var can be removed in those files.

2) Introduce a filegroup, core_public_api_files, that can be used
from frameworks/base/ rather than "internal" variables defined in
non_openjdk_java_files.bp, openjdk_java_files.bp and conscrypt.

Bug: 126332291
Test: build only
Merged-In: I3c85d17dd7405e65a6be9e60831b1a07e4f08abf
Change-Id: I3c85d17dd7405e65a6be9e60831b1a07e4f08abf
diff --git a/JavaLibrary.bp b/JavaLibrary.bp
index 2d26422..e763224 100644
--- a/JavaLibrary.bp
+++ b/JavaLibrary.bp
@@ -56,7 +56,7 @@
     srcs: [":openjdk_java_files"],
 }
 
-// OpenJDK source is not annotated with @hide so we need a separate
+// OpenJDK source is not annotated with @hide so we need this separate
 // filegroup for just the parts that contribute to the API.
 filegroup {
     name: "core_oj_api_files",
@@ -72,7 +72,7 @@
     ],
 }
 
-// Some parts of libart are not annotated with @hide so we need a separate
+// Some parts of libart are not annotated with @hide so we need this separate
 // filegroup for just the parts that contribute to the API.
 filegroup {
     name: "core_libart_api_files",
@@ -82,14 +82,26 @@
     ],
 }
 
+// The set of files for the core library that have been marked up with @hide
+// for the public SDK APIs. Used from frameworks/base/ to indicate the source
+// files for inclusion in the public SDK docs.
+filegroup {
+    name: "core_public_api_files",
+    srcs: [
+        ":core_oj_api_files",
+        ":core_libart_api_files",
+        ":conscrypt_public_api_files",
+    ],
+}
+
 // The set of files for the core library that have been marked up with @hide and
 // API-related annotations. Note that this includes the intra-core and
 // core-platform APIs as well as the public APIs.
 //
-// Some source files in :openjdk_mmodule_extra_files are annotated by applying
-// annotations to the .annotated.java stubs files in ojluni/annotated/mmodules
-// and rather than in the original source. See the comments in
-// openjdk_java_files.bp for more details.
+// Some source files in :core_oj_api_files and :openjdk_mmodule_extra_files are
+// annotated by applying annotations to the .annotated.java stubs files in
+// ojluni/annotated/mmodules and rather than in the original source. See the comments
+// in openjdk_java_files.bp for more details.
 filegroup {
     name: "core_api_files",
     srcs: [