Replace fetch_content by find_package for p2300 package

cmake/pika_setup_p2300.cmake

@@ -11,39 +11,6 @@ if(PIKA_WITH_P2300_REFERENCE_IMPLEMENTATION AND NOT PIKA_FIND_PACKAGE)
     )
   endif()
 
-  include(FetchContent)
-
-  fetchcontent_declare(
-    P2300
-    GIT_REPOSITORY https://github.com/brycelelbach/wg21_P2300_std_execution.git
-    GIT_TAG 063fd9a9e8d9c0284f795f5342e057b3bc428202
-  )
-  fetchcontent_getproperties(P2300)
-  if(NOT p2300_POPULATED)
-    fetchcontent_populate(P2300)
-  endif()
-
-  add_library(P2300 INTERFACE)
-  target_include_directories(
-    P2300 SYSTEM INTERFACE "$<BUILD_INTERFACE:${p2300_SOURCE_DIR}/include>"
-                           "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
-  )
-  target_compile_features(P2300 INTERFACE cxx_std_20)
-
-  install(
-    TARGETS P2300
-    EXPORT pika_internal_targets
-    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT core
-  )
-  pika_export_internal_targets(P2300)
-
-  install(
-    DIRECTORY "${p2300_SOURCE_DIR}/include/"
-    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
-    COMPONENT core
-  )
-
-  target_link_libraries(pika_base_libraries INTERFACE P2300)
+  find_package(p2300 QUIET)
+  target_link_libraries(pika_base_libraries INTERFACE P2300::p2300)
 endif()