Make internal runtimescheduler headers private

Summary:
Switch `primitives.h`, `RuntimeScheduler_Legacy.h` and `RuntimeScheduler_Modern.h` in `react/renderer/runtimescheduler` to `PrivateGuard.h`. They are implementation details of `RuntimeScheduler` and `RuntimeSchedulerBinding`, included only from the module's own sources.

Changelog: [Internal]

Differential Revision: D123414260

Author: j-piasecki

packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Legacy.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <react/cxxstableapi/FrameworksGuard.h>
+#include <react/cxxstableapi/PrivateGuard.h>
 
 #ifndef RCT_REMOVE_LEGACY_ARCH
 

packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Modern.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <react/cxxstableapi/FrameworksGuard.h>
+#include <react/cxxstableapi/PrivateGuard.h>
 
 #include <React/RuntimeExecutor.h>
 #include <react/renderer/runtimescheduler/RuntimeScheduler.h>

packages/react-native/ReactCommon/react/renderer/runtimescheduler/primitives.h

@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <react/cxxstableapi/FrameworksGuard.h>
+#include <react/cxxstableapi/PrivateGuard.h>
 
 #include <jsi/jsi.h>
 #include <react/renderer/runtimescheduler/Task.h>