cmake: add integration tests, run them in CI

Add CMake test project consuming curl via these methods:
`FetchContent`, `add_subdirectory()`, `find_package()`.

Also:
- GHA/distcheck: run these tests in CI.
- cmakelint: exclude a warning for calling "wonky-cased" built-in
  CMake functions, such as `FetchContent_Declare()`.

Closes #16126

CMake/Utilities.cmake

@@ -47,7 +47,7 @@ function(curl_dumpvars)
     if(_var_advanced)
       set(_var_advanced " [adv]")
     endif()
-    message("${_var}${_var_type}${_var_advanced} = ${${_var}}")
+    message("${_var}${_var_type}${_var_advanced} = '${${_var}}'")
   endforeach()
   message("::endgroup::")
 endfunction()