Separate cc_library_headers to its own file and add tests

Preparation for adding cc_library_headers to sdk.

Bug: 148933848
Test: m nothing
Change-Id: Icbc86b21f44dc79393b82be339cf3b133cbf9d8c

Android.bp

@@ -207,6 +207,7 @@ bootstrap_go_package {
         "cc/binary_sdk_member.go",
         "cc/fuzz.go",
         "cc/library.go",
+        "cc/library_headers.go",
         "cc/library_sdk_member.go",
         "cc/object.go",
         "cc/test.go",
@@ -232,6 +233,7 @@ bootstrap_go_package {
         "cc/compiler_test.go",
         "cc/gen_test.go",
         "cc/genrule_test.go",
+        "cc/library_headers_test.go",
         "cc/library_test.go",
         "cc/object_test.go",
         "cc/prebuilt_test.go",