[Phi] Extend implementation to use GQA/MQA. (#28163)
* chore(phi): Updates configuration_phi with missing keys.
* chore(phi): Adds first draft of combined modeling_phi.
* fix(phi): Fixes according to latest review.
* fix(phi): Removes pad_vocab_size_multiple to prevent inconsistencies.
* fix(phi): Fixes unit and integration tests.
* fix(phi): Ensures that everything works with microsoft/phi-1 for first integration.
* fix(phi): Fixes output of docstring generation.
* fix(phi): Fixes according to latest review.
* fix(phi): Fixes according to latest review.
* fix(tests): Re-enables Phi-1.5 test.
* fix(phi): Fixes attention overflow on PhiAttention (for Phi-2).
* fix(phi): Improves how queries and keys are upcast.
* fix(phi): Small updates on latest changes.
