Avoid importing all models when instantiating a pipeline
# What does this PR do?

The check on the model being in the right mapping for the pipeline requires the import of all models associated with that pipeline. This is because it uses the `MODEL_XXX_MAPPING` instead of the `MODEL_XXX_MAPPING_NAMES`. This PR suggests to switch to that, since the check is done on the model name anyway, to avoid weird warnings unrelevant to the user (for instance #24903 gives one example, I also end up having some logs of CUDA kernel being built on my side).

The only feature of the `MODEL_XXX_MAPPING` we need to keep compared to `MODEL_XXX_MAPPING_NAMES` is the extra content (coming from model on the Hub), so this PR adds a reference from the mapping names to the mapping.

Fixes #24903
_The documentation is not available anymore as the PR was closed or merged._<|||||>It works too, but I think with the design selected for the PEFT integration in `from_pretrained` (which will supercede #24827), we won't need to remove them. I think it's a useful warning to have when users try to instantiate a pipeline with a model not suitable for it.