[cmake] Fix standalone configuration of examples project (#6079)

Configuring examples/ as a standalone project (cd examples && cmake .)
failed with 'Unknown CMake command add_if_flag_compiles' and a missing
cmake_minimum_required() error on CMake 4.x.

- Add cmake_minimum_required(VERSION 3.22), matching the root project
- Include raylib's AddIfFlagCompiles helper via ../cmake
- Default PLATFORM to Desktop when not inherited from the raylib build

examples/CMakeLists.txt

@@ -1,6 +1,18 @@
 # Setup the project and settings
+cmake_minimum_required(VERSION 3.22)
 project(examples)
 
+# Include raylib's cmake helper functions, so the examples can also be
+# configured standalone (`cd examples && cmake .`) and not only as part
+# of the raylib project.
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/../cmake")
+include(AddIfFlagCompiles)
+
+# Default to the Desktop platform when configured standalone.
+if (NOT DEFINED PLATFORM)
+    set(PLATFORM "Desktop" CACHE STRING "Platform to build examples for")
+endif ()
+
 # Directories that contain examples
 set(example_dirs
     audio