DocTypeDeclCtx is missing CLOSE from the type definition

[hornta]

The type declaration is missing their CLOSE token from the api.d.ts
https://github.com/SAP/xml-tools/blob/master/packages/parser/api.d.ts#L98

[kddnewton]

Also adding:

• ContentCstNode children is missing { PROCESSING_INSTRUCTION: IToken[] }
• ExternalIDNode name should be "externalID"
• Almost all of the values should be listed as optional even though they're currently mandatory