A conversion of the OpenAI OpenAPI to TypeSpec

Snapshot: https://raw.githubusercontent.com/openai/openai-openapi/28a300c5784415af66f81b2acc0db182f6eb3bbd/openapi.yaml

There are some deltas:

Changes to API Semantics

Many things are missing defaults (mostly due to bug where we can't set null defaults)
Error responses have been added.
Where known, the object property's type is narrowed from string to the constant value it will always be

Changes to API metadata or OpenAPI format

Much of the x-oaiMeta entries have not been added.
In some cases, new schemas needed to be defined in order to be defined in TypeSpec (e.g. because the constraints could not be added to a model property with a heterogeneous type)
There is presently no way to set title