Introduce `VulkanDelegateHeader` to manage constant data and shader data (#2013)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2013

## Context

This changeset is essentially a mirror of https://github.com/pytorch/executorch/pull/1523 in the XNNPACK delegate which is the first step to enabling constant weight data to be serialized outside the flatbuffer blob to speed up deserialization time for large models.

`VulkanDelegateHeader` is introduced which will be used later on to help interpret what different sections of the serialized binary blob corresponds to. The primary difference compared to `XNNHeader` which was added for the XNNPACK delegate is that fields are added to support custom compute shaders that will be serialized with the model.
ghstack-source-id: 215799821
exported-using-ghexport

Reviewed By: mcr229

Differential Revision: D53957853

fbshipit-source-id: 233e8e58d5b8fc9777313f188748f5ee60c83726