Heading blocks do not have the is_toggleable property in their types

[huw]

The specification says that heading_1, heading_2, and heading_3 blocks should have an is_toggleable property within the heading_x property. I have verified against the API that it is reporting this data correctly (and therefore returning it through the client), but it is not typed correctly in the library.

While it is present inside BlockObjectRequest, BlockObjectRequestWithoutChildren, UpdateBlockBodyParameters, it is not present inside BlockObjectResponse (specifically Heading1BlockObjectResponse, Heading2BlockObjectResponse, and Heading3BlockObjectResponse). I’d normally submit a PR but I’m aware that api-endpoints.ts is auto-generated; I’ve patched the library for my own usage.

This is somewhat related to #245, although I believe @aalemayhu was using a version of the API before the is_toggleable property was included in the response.

[aalemayhu]

I was not aware of is_toggleable, Thanks!