`AmazonBedrockChatGenerator` - move multimodal support from experimental

Haystack 2.16.0 will introduce general support for multimodal features.

After the release, we should move the multimodal support for Bedrock from [experimental](https://github.com/deepset-ai/haystack-experimental/blob/main/haystack_experimental/components/generators/chat/amazon_bedrock.py) to the core integrations.