Improve schema names and comments (#2035)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2035

This change addresses a lot of nitpicks which improves readability (at least for me):
- Improve schema comments to be sentences and limit line length.
- Use the suffix `_id` and `_ids` for an index and list of indices, respectively.
- Order of tables matches their usage in `table VkGraph`.
- Improve understanding of python dict contents via name change: `node_vk_value_ids` -> `node_to_value_ids`.

Note we will remove `VkArithmeticOpType` soon, so we don't bother improving its readability.

Reviewed By: SS-JIA

Differential Revision: D53982444

fbshipit-source-id: 7bf345d93d1450bee89713a55470da8cb14a2155