…dapters into dev/test-refactoring

- reorder directory structure to separate testing models and adapter methods (needs further refactoring for separating tests that are extecuted for each model vs tests that are just run once)
- remove all model tests except albert for now (will be readded once final design is agreed on)
- refactor albert adapter test class to group test mixins in categories which are then displayed accordingly by test viewer
- adjust imports to reflect new directory structure

- refactor generate_test into base test class and adapt parallel generate test accordingly
- refactor lm head selection into own method
- create utils file for utility methods and adapt imports accordingly
- remove is_speech_model flags
- replace redundant attributes and methods
- enforce proper method naming conventions

This reverts commit b390d61.

- Re-add bart adapter method tests
- Remove duplicate added tests
- In conversion test refactor model specific if else statements into model test class

- deberta
- debertav2
- distilbert
- electra
- encoder-decoder
- llama
- mbart
- mistral
- mt5
- plbart
- roberta