CMake: Add build option to disable experimental features

This adds an option `WITH_EXPERIMENTAL_FEATURES` which is `ON` by default.
Sometimes it's usefull to be able to turn off all experimental features
during development for testing purposes. This option is still enforced to be
`OFF` for release cycles other than `alpha`.

Pull Request: https://projects.blender.org/blender/blender/pulls/118513

CMakeLists.txt

@@ -781,8 +781,10 @@ if(WIN32)
   option(WITH_TBB_MALLOC_PROXY "Enable the TBB malloc replacement" ON)
 endif()
 
+option(WITH_EXPERIMENTAL_FEATURES "Enable experimental features" ON)
+
 # This should be turned off when Blender enter beta/rc/release
-if("${BLENDER_VERSION_CYCLE}" STREQUAL "alpha")
+if("${BLENDER_VERSION_CYCLE}" STREQUAL "alpha" AND WITH_EXPERIMENTAL_FEATURES)
   set(WITH_EXPERIMENTAL_FEATURES ON)
 else()
   set(WITH_EXPERIMENTAL_FEATURES OFF)

source/blender/blenloader/CMakeLists.txt

@@ -133,3 +133,7 @@ if(WITH_GTESTS)
   )
   blender_add_test_suite_lib(blenloader "${TEST_SRC}" "${INC}" "${INC_SYS}" "${TEST_LIB}")
 endif()
+
+if(WITH_EXPERIMENTAL_FEATURES)
+  add_definitions(-DWITH_EXPERIMENTAL_FEATURES)
+endif()

source/blender/blenloader/intern/versioning_userdef.cc

@@ -953,10 +953,11 @@ void BLO_sanitize_experimental_features_userpref_blend(UserDef *userdef)
    *
    * At that time master already has its version bumped so its user preferences
    * are not touched by these settings. */
-
+#ifdef WITH_EXPERIMENTAL_FEATURES
   if (BKE_blender_version_is_alpha()) {
     return;
   }
+#endif
 
   MEMSET_STRUCT_AFTER(&userdef->experimental, 0, SANITIZE_AFTER_HERE);
 }