[Flax] Fix hybrid clip
# What does this PR do?

This PR fixes an issue with saving and loading `HybridCLIPConfig` which was causing issues when loading the model.

The config was expecting the `text_config_dict` and `vision_config_dict` arguments, but in the `to_dict` it was saved as `text_config` and `vision_config`. So the next time when `config` was loaded using `from_pretrained` the `model_type` key was missing from `text_config_dict` and `vision_config_dict` as we pop that in the init.

This PR renames `text_config_dict` and `vision_config_dict` to `text_config` and `vision_config` respectively. This is slightly breaking as we won't be able to load previously saved configs. A simple workaround for that is to re-initialize the config using
`from_text_vision_configs` method and resave them.

This PR also adds some usage examples for `FlaxHybridCLIP`.

Fixes #12513

(I should really add tests for this)