Add logic to build the shared libs and srcaars for the non-App libraries.

Adds a helper function to build the "empty" shared libraries used by the non-App libraries. Changes how the C++ proguard file is defined to use a target. Changes the aar generation code to rely more on the targets, and using generator expressions.

PiperOrigin-RevId: 280502793

Author: a-maurice

cmake/firebase_cpp_gradle.cmake

@@ -44,9 +44,14 @@ function(firebase_cpp_proguard_file LIBRARY_NAME)
   string(TOUPPER "${LIBRARY_NAME}" upper_name)
   set(proguard_var "FIREBASE_CPP_${upper_name}_PROGUARD")
   set(${proguard_var}
-      "${FIREBASE_SOURCE_DIR}/${LIBRARY_NAME}/build/${LIBRARY_NAME}.pro")
-  set("${proguard_var}" "${${proguard_var}}" PARENT_SCOPE)
+      "${FIREBASE_SOURCE_DIR}/${LIBRARY_NAME}/build/${LIBRARY_NAME}.pro"
+      CACHE FILEPATH "Proguard file for ${LIBRARY_NAME}" FORCE)
 
   firebase_cpp_gradle(":${LIBRARY_NAME}:externalNativeBuildRelease"
                       "${${proguard_var}}")
+
+  add_custom_target(
+    "${LIBRARY_NAME}_cpp_proguard"
+    DEPENDS ${${proguard_var}}
+  )
 endfunction()