Alignment: use a simplified ragged type for performance

[danieldk]

Description

This introduces the AlignmentArray type, which is a simplified version of Ragged that performs better on the simple(r) indexing performed for alignment.

When training a biaffine parser pipeline with morphology and tagging on a GPU, this speeds up training by about 19%. This should improve performance for all TrainablePipes that use get_alignment to get gold standard annotations.

Types of change

Performance improvement.

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[danieldk]

Out of draft: trained a transformer model and didn't see any regressions in accuracy.

[adrianeboyd]

Also tested on a full set of trained pipeline builds.