Expose nvgCreateBgfxTexture() helper function (#3046)

The nvgCreateBgfxTexture() helper function is already implemented in
the nanovg wrapper library, so its useful to expose this function
to the user.

Also expose the NVG_IMAGE_NODELETE flag so this can be passed to the
nvgCreateBgfxTexture() function, to indicate that the caller retains
ownership of the bgfx texture.

examples/common/nanovg/nanovg_bgfx.cpp

@@ -58,11 +58,6 @@ namespace
 		NSVG_SHADER_IMG
 	};
 
-	// These are additional flags on top of NVGimageFlags.
-	enum NVGimageFlagsGL {
-		NVG_IMAGE_NODELETE = 1<<16, // Do not delete GL texture handle.
-	};
-
 	struct GLNVGtexture
 	{
 		bgfx::TextureHandle id;

examples/common/nanovg/nanovg_bgfx.h

@@ -20,6 +20,11 @@ struct NVGLUframebuffer
   bgfx::ViewId viewId;
 };
 
+// These are additional flags on top of NVGimageFlags.
+enum NVGimageFlagsGL {
+	NVG_IMAGE_NODELETE = 1<<16, // Do not delete GL texture handle.
+};
+
 ///
 NVGcontext* nvgCreate(int32_t _edgeaa, bgfx::ViewId _viewId, bx::AllocatorI* _allocator);
 
@@ -76,4 +81,7 @@ void nvgluDeleteFramebuffer(NVGLUframebuffer* _framebuffer);
 ///
 void nvgluSetViewFramebuffer(bgfx::ViewId _viewId, NVGLUframebuffer* _framebuffer);
 
+///
+int nvgCreateBgfxTexture(struct NVGcontext *_ctx, bgfx::TextureHandle _id, int _width, int _height, int _flags);
+
 #endif // NANOVG_BGFX_H_HEADER_GUARD