Support IP Adapter weight loading for StableDiffusionXLControlNetInpaintPipeline

[nkaewam]

What does this PR do?

Fixes #6866 and also an extension of PR: #6941

Added IPAdapterMixin loader to StableDiffusionXLControlNetInpaintPipeline to allow for .load_ip_adapter in pipeline.

Example snippet code:

image_encoder = CLIPVisionModelWithProjection.from_pretrained(
            "h94/IP-Adapter",
            subfolder="models/image_encoder",
            torch_dtype=torch.float16,
            cache_dir=CACHE_DIR
).to(device)


pipe = StableDiffusionXLControlNetInpaintPipeline.from_pretrained(
            weight_path,
            cache_dir=CACHE_DIR,
            vae=sd_vae,
            controlnet=controlnet, 
            image_encoder=image_encoder,
            torch_dtype=torch.float16
).to(device)
 
# this PR allows this to be possible      
pipe.load_ip_adapter("h94/IP-Adapter", subfolder="sdxl_models", weight_name="ip-adapter-plus_sdxl_vit-h.safetensors", cache_dir=CACHE_DIR)

images = pipe(
            image=room_image,
            ip_adapter_image=style_image, 
            control_image=control_image, 
            mask_image=mask_image,
            ...other-params
).images

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