Internal header file included in dmsdk

**Describe the bug (REQUIRED)**
Since version 1.9.4 (#8743), [`dmsdk/graphics/graphics.h`](https://github.com/defold/defold/blob/1.9.4/engine/graphics/src/dmsdk/graphics/graphics.h) needs to include `graphics/graphics_ddf.h`, which is not part of the sdk but seems to be an internal file, causing errors for users who previously used dmsdk to get type hints and autocompletion in the IDE.

**To Reproduce (REQUIRED)**
Steps to reproduce the behavior:
1. Download `defoldsdk_headers.zip` from releases
2. Extract `defoldsdk/sdk/include/dmsdk` folder to some include paths (for example `/usr/local/include`)
3. In a IDE with C++ support write `#include `
4. See error

**Expected behavior (REQUIRED)**
No error should be reported in IDE, as it was before 1.9.4.

**Defold version (REQUIRED):**
- 1.9.4 and after

**Platforms (REQUIRED):**
Unrelated

**Workaround (OPTIONAL):**
1. Add `defoldsdk/include` folder to the include path to make `#include ` work, but that's generally not a good idea.
2. Modify `dmsdk/graphics/graphics.h` to remove the include line and restore the previous definition of [`VertexStepFunction`](https://github.com/defold/defold/blob/f9e7badded4034a6567c16ac2150d25b4d023659/engine/graphics/src/dmsdk/graphics/graphics.h#L490-L501).

**Additional context (OPTIONAL):**
This was originally posted at https://forum.defold.com/t/internal-header-file-included-in-dmsdk/79316.