cmake: Integrate DiscoverTests and normalize test names

Updates the build system to use the new DiscoverTests module.
This also standardizes test names to use dot-separated parts for
consistency.

examples/CMakeLists.txt

@@ -8,8 +8,7 @@ function(add_example name)
     secp256k1
     $<$<PLATFORM_ID:Windows>:bcrypt>
   )
-  set(test_name ${name}_example)
-  add_test(NAME secp256k1_${test_name} COMMAND ${target_name})
+  add_test(NAME secp256k1.example.${name} COMMAND ${target_name})
 endfunction()
 
 add_example(ecdsa)