The new JS build for Ink uses the allowDeclareFields option for

@babel/preset-typescript, which will preserve any fields which are not

marked with declare (initializing to undefined). This caused our

type definitions to shadow the prototypeAttrs copied over by spina.
allowDeclareFields is the correct forward-looking thing to use, and

will be the default in Babel 8. This change fixes the resulting issue by

changing our type-only definitions to properly use declare.

Ran unit tests.
Verified that things like the dialog title worked again.