Use spdlog_vendor in place of spdlog

[azeey]

spdlog is not being properly found on ROS windows builds. Example: https://ci.ros2.org/view/nightly/job/nightly_win_rel/3158/cmake/new/. This will replace instances of spdlog in the upstream package with spdlog_vendor.

Running this on gz-utils at 3c58be65f5d56fbab2bad1a01a45841d71666448 with #8 and #7 merged generates the following diff that matches gazebo-release/gz_utils_vendor#6:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4286745..bc17303 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,6 +21,7 @@ find_package(ament_cmake_vendor_package REQUIRED)
 find_package(ament_cmake_export_dependencies REQUIRED)
 
 find_package(gz_cmake_vendor REQUIRED)
+find_package(spdlog_vendor REQUIRED)
 
 # Set the VERSION_MATCH to "EXACT" by default, but relax the requirement
 # if we are users are building from source (determined by the
@@ -57,6 +58,7 @@ endif()
 
 ament_export_dependencies(
   gz_cmake_vendor
+  spdlog_vendor
 )
 
 if(NOT ${${LIB_NAME_FULL}_FOUND})
diff --git a/package.xml b/package.xml
index 81050e0..45adfd7 100644
--- a/package.xml
+++ b/package.xml
@@ -24,9 +24,8 @@
   <buildtool_depend>ament_cmake_test</buildtool_depend>
   <buildtool_depend>ament_cmake_vendor_package</buildtool_depend>
 
-  <build_depend>spdlog</build_depend>
-  <exec_depend>spdlog</exec_depend>
   <depend>gz_cmake_vendor</depend>
+  <depend>spdlog_vendor</depend>
 
   <!-- Depend on the package we are vendoring to allow building it from source -->
   <depend condition="$GZ_BUILD_FROM_SOURCE != ''">gz-utils3</depend>

more context: gazebosim/gz-utils#146