Make ORT and Dawn use the same protobuf/abseil source code (#23447)

### Description
Make ORT and Dawn use the same protobuf/abseil source code

Author: Changming Sun

cmake/external/abseil-cpp.cmake

@@ -32,7 +32,13 @@ FetchContent_Declare(
 
 onnxruntime_fetchcontent_makeavailable(abseil_cpp)
 FetchContent_GetProperties(abseil_cpp)
-set(ABSEIL_SOURCE_DIR ${abseil_cpp_SOURCE_DIR})
+if(abseil_cpp_SOURCE_DIR)
+  set(ABSEIL_SOURCE_DIR ${abseil_cpp_SOURCE_DIR})
+  if(onnxruntime_USE_WEBGPU)
+    set(DAWN_ABSEIL_DIR ${abseil_cpp_SOURCE_DIR})
+  endif()
+endif()
+
 # abseil_cpp_SOURCE_DIR is non-empty if we build it from source
 message(STATUS "Abseil source dir:" ${ABSEIL_SOURCE_DIR})
 # abseil_cpp_VERSION  is non-empty if we find a preinstalled ABSL

cmake/external/onnxruntime_external_deps.cmake

@@ -222,6 +222,11 @@ onnxruntime_fetchcontent_makeavailable(Protobuf)
 if(Protobuf_FOUND)
   message(STATUS "Protobuf version: ${Protobuf_VERSION}")
 else()
+  if(protobuf_SOURCE_DIR)
+    if(onnxruntime_USE_WEBGPU)
+      set(DAWN_PROTOBUF_DIR ${protobuf_SOURCE_DIR})
+    endif()
+  endif()
   # Adjust warning flags
   if (TARGET libprotoc)
     if (NOT MSVC)