Alleviate CMake target name clashes, visibility, and grouping.

Simplify <platform>_generate cmake function signature, as TARGET_ALIAS and TARGET_NAME are still in scope and do not need to be passed.
Add USE_FOLDERS, and FOLDER properties to group targets in VS and XCode
Guard test target with GODOT_ENABLE_TESTING
Generate all three variants in the form godot-cpp.test.<target> to remove the -DTEST_TARGET option clutter.
Update the docs/cmake.rst with information about the testing target
Update the Github CI

CMakeLists.txt

@@ -38,6 +38,7 @@ The CMake equivalent is below.
 ]=======================================================================]
 
 include( cmake/godotcpp.cmake )
+
 godotcpp_options()
 
 #[[ Python is required for code generation ]]
@@ -53,5 +54,12 @@ project( godot-cpp
 compiler_detection()
 godotcpp_generate()
 
-# Test Example
-add_subdirectory( test )
+# Conditionally enable the godot-cpp.test.<target> integration testing targets
+if( GODOT_ENABLE_TESTING )
+    add_subdirectory( test )
+endif()
+
+# If this is the top level CMakeLists.txt, Generators which honor the
+# USE_FOLDERS flag will organize godot-cpp targets under the subfolder
+# 'godot-cpp'. This is enable by default from CMake version 3.26
+set_property(GLOBAL PROPERTY USE_FOLDERS ON)