ebiten: add info to know how much memory is allocated for GPU textures

[hajimehoshi]

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• OpenBSD
• Android
• iOS
• Nintendo Switch
• PlayStation 5
• Xbox
• Web Browsers

What feature would you like to be added?

Go's GC doesn't recognize allocated memory for GPU. For example, an object handling a GPU texture (*ebiten.Image), and GC recognizes the memory usage of the object as only a struct size. Thus, image objects don't pressure GC, and this tends to cause memory bloat on GPU, even though too many (no-longer-referred) images are created. This is a serious problem especially in some devices that have unified memory for CPU and GPU.

At least, we want a way to know texture memory usages. Let's add an API to DebugInfo

/CC @wasedaigo

Why is this needed?

In order to get hints to improve memory usages. Especially this matters in some special devices that have unified memory for CPU and GPU.

[hajimehoshi]

type DebugInfo struct {
    ...

    // TotalGPUImageMemoryUsageInBytes is the total image memory usage for GPU in bytes.
    // TotalGPUImageMemoryUsageInBytes is approximately the total memory usage for GPU.
    TotalGPUImageMemoryUsageInBytes int64
}

Do we need each image info?

[hajimehoshi]

#2207 is related.