Switch header convention from #include "SDL.h" to #include <SDL3/SDLh>

I ran this script in the include directory:
```sh
sed -i '' -e 's,#include "\(SDL.*\)",#include <SDL3/\1>,' *.h
```

I ran this script in the src directory:
```sh
for i in ../include/SDL3/SDL*.h
do hdr=$(basename $i)
   if [ x"$(echo $hdr | egrep 'SDL_main|SDL_name|SDL_test|SDL_syswm|SDL_opengl|SDL_egl|SDL_vulkan')" != x ]; then
        find . -type f -exec sed -i '' -e 's,#include "\('$hdr'\)",#include <SDL3/\1>,' {} \;
    else
        find . -type f -exec sed -i '' -e '/#include "'$hdr'"/d' {} \;
    fi
done
```

Fixes https://github.com/libsdl-org/SDL/issues/6575

include/SDL3/SDL_gesture.h

@@ -0,0 +1,117 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2022 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+/**
+ *  \file SDL_gesture.h
+ *
+ *  Include file for SDL gesture event handling.
+ */
+
+#ifndef SDL_gesture_h_
+#define SDL_gesture_h_
+
+#include <SDL3/SDL_stdinc.h>
+#include <SDL3/SDL_error.h>
+#include <SDL3/SDL_video.h>
+
+#include <SDL3/SDL_touch.h>
+
+
+#include <SDL3/begin_code.h>
+/* Set up for C function definitions, even when using C++ */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef Sint64 SDL_GestureID;
+
+/* Function prototypes */
+
+/**
+ * Begin recording a gesture on a specified touch device or all touch devices.
+ *
+ * If the parameter `touchId` is -1 (i.e., all devices), this function will
+ * always return 1, regardless of whether there actually are any devices.
+ *
+ * \param touchId the touch device id, or -1 for all touch devices
+ * \returns 1 on success or 0 if the specified device could not be found.
+ *
+ * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_GetTouchDevice
+ */
+extern DECLSPEC int SDLCALL SDL_RecordGesture(SDL_TouchID touchId);
+
+
+/**
+ * Save all currently loaded Dollar Gesture templates.
+ *
+ * \param dst a SDL_RWops to save to
+ * \returns the number of saved templates on success or 0 on failure; call
+ *          SDL_GetError() for more information.
+ *
+ * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_LoadDollarTemplates
+ * \sa SDL_SaveDollarTemplate
+ */
+extern DECLSPEC int SDLCALL SDL_SaveAllDollarTemplates(SDL_RWops *dst);
+
+/**
+ * Save a currently loaded Dollar Gesture template.
+ *
+ * \param gestureId a gesture id
+ * \param dst a SDL_RWops to save to
+ * \returns 1 on success or 0 on failure; call SDL_GetError() for more
+ *          information.
+ *
+ * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_LoadDollarTemplates
+ * \sa SDL_SaveAllDollarTemplates
+ */
+extern DECLSPEC int SDLCALL SDL_SaveDollarTemplate(SDL_GestureID gestureId,SDL_RWops *dst);
+
+
+/**
+ * Load Dollar Gesture templates from a file.
+ *
+ * \param touchId a touch id
+ * \param src a SDL_RWops to load from
+ * \returns the number of loaded templates on success or a negative error code
+ *          (or 0) on failure; call SDL_GetError() for more information.
+ *
+ * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_SaveAllDollarTemplates
+ * \sa SDL_SaveDollarTemplate
+ */
+extern DECLSPEC int SDLCALL SDL_LoadDollarTemplates(SDL_TouchID touchId, SDL_RWops *src);
+
+/* Ends C function definitions when using C++ */
+#ifdef __cplusplus
+}
+#endif
+#include <SDL3/close_code.h>
+
+#endif /* SDL_gesture_h_ */
+
+/* vi: set ts=4 sw=4 expandtab: */