Renaming TextEncoder -> LLMEncoder

[rcap107]

This PR renames the TextEncoder to LLMEncoder.

I renamed all instances of TextEncoder (with the exception of what's in the changelog), added a deprecation warning and the relative test.

Since I had to modify the content of the _text_encoder.py file, I thought it would be better to first merge this PR and then open a separate PR to rename the file, to keep the diff simple.

[GaelVaroquaux]

One small comment, but that may be of importance

[GaelVaroquaux]

A better way of doing this is to use the deprecated decorator of scikit-learn: https://scikit-learn.org/stable/modules/generated/sklearn.utils.deprecated.html
Something like:

Suggested change

	class TextEncoder(LLMEncoder):
	"""
	Deprecated: Use :class:`~skrub.LLMEncoder` instead.
	.. deprecated:: 0.11
	The ``TextEncoder`` has been renamed to ``LLMEncoder``, and will be removed
	in a future release.
	"""
	def __init__(self, *args, **kwargs):
	import warnings
	warnings.warn(
	"TextEncoder is deprecated and will be removed in a future release. "
	"Use LLMEncoder instead.",
	DeprecationWarning,
	stacklevel=2,
	)
	super().__init__(*args, **kwargs)
	@deprecated("TextEncoder has been renamed to LLMEncoder and will be removed in version 0.12.")
	class TextEncoder(LLMEncoder):
	pass

I believe that this is important to avoid the use of "*args, **kwargs", which don't play well with our detection of arguments for get_params/set_params