UITemplateProcessor: Fix case of include path (facebook#22239)

Summary:
This pull request fixes a path name to be a proper case in `UITemplateProcessor`, which fixes this build warning:

```
{snip}/react/uimanager/UITemplateProcessor.cpp:17:10: warning: non-portable path to file '<react/core/ComponentDescriptor.h>';
      specified path differs in case from file name on disk [-Wnonportable-include-path]
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         <react/core/ComponentDescriptor.h>
1 warning generated.
```
Pull Request resolved: facebook#22239

Differential Revision: D13020871

Pulled By: shergin

fbshipit-source-id: 77555018cd569880518ff884ed8768effc4ea97e

ReactCommon/fabric/uimanager/UITemplateProcessor.cpp

@@ -14,7 +14,7 @@
 #include <react/components/view/ViewShadowNode.h>
 #include <react/core/LayoutContext.h>
 #include <react/core/ShadowNodeFragment.h>
-#include <react/core/componentDescriptor.h>
+#include <react/core/ComponentDescriptor.h>
 #include <react/debug/DebugStringConvertible.h>
 #include <react/debug/DebugStringConvertibleItem.h>