Use common convention for EXPORT name (ros2#1797) (ros2#1888)

As @JafarAbdi pointed out in [this PR](moveit/srdfdom#96 (comment)) the _exports suffix is non-standard.  `Targets` or `-targets` is used by gtest, fmt, and nlohmann_json.

I copied the _exports suffix into the moveit2 repo and now regret it.  It would be nice to use common conventions here so others don't make the same mistake.

(cherry picked from commit 1c5fc42)

Co-authored-by: Tyler Weaver <[email protected]>

Author: mergify[bot]

source/Guides/Ament-CMake-Documentation.rst

@@ -131,7 +131,7 @@ When building a reusable library, some information needs to be exported for down
 
 .. code-block:: cmake
 
-    ament_export_targets(export_my_library HAS_LIBRARY_TARGET)
+    ament_export_targets(my_libraryTargets HAS_LIBRARY_TARGET)
     ament_export_dependencies(some_dependency)
 
     install(
@@ -141,7 +141,7 @@ When building a reusable library, some information needs to be exported for down
 
     install(
       TARGETS my_library
-      EXPORT export_my_library
+      EXPORT my_libraryTargets
       LIBRARY DESTINATION lib
       ARCHIVE DESTINATION lib
       RUNTIME DESTINATION bin
@@ -183,7 +183,7 @@ Here is what's happening in the snippet above:
   It installs the CMake files for the ``my_library`` target.
   It is named exactly like the argument in ``ament_export_targets`` and could be named like the library.
   However, this will then prohibit using the ``ament_target_dependencies`` way of including your library.
-  To allow for full flexibility, it is advised to prepend the export target with something like ``export_<target>``.
+  To allow for full flexibility, it is advised to prepend the export target with something like ``<target>Targets``.
 
 - All install paths are relative to ``CMAKE_INSTALL_PREFIX``, which is already set correctly by colcon/ament