[`Vision`] [Refactor] Initialize weights on the correct place
# What does this PR do?

This PR forces some modules to be initialised on the correct place (i.e. on the `_init_weights` method). 
With more vision models being added, contributors are copying the practice to initialise some weights outside `_init_weights`. I think that we should centralize weights initialisation on the `_init_weights` method, by applying this on most-copied / downloaded models.

Related:
- https://github.com/huggingface/transformers/pull/20716#discussion_r1049764368 
_The documentation is not available anymore as the PR was closed or merged._