Move PublicMethodsOf into @kbn/utility-types

[rudolf]

Core uses the global PublicMethodsOf utility type in several places, we should move this to @kbn/utility-types and import it instead of using the global.

We mostly use this type to get the public contract of a class. Usually this means getting the public methods but there are a few classes which expose public properties which this helper misses.

So I propose we create a PublicContractOf helper instead:

export type PublicContractOf<T> = Pick<T, keyof T>

[elasticmachine]

Pinging @elastic/kibana-platform

[mshustov]

+1 the current solution breaks typings, because PublicMethodsOf is src/ and in x-pack are different types.
Does it make sense to move all types from https://github.com/restrry/kibana/blob/f783d48301ff01cec7df163bea0b4adc8dd26422/typings/index.d.ts ?

[streamich]

+1, and maybe we can call it:

type PublicKeys<T> = keyof T;
type PublicContract<T> = Pick<T, PublicKeys<T>>

[rudolf]

Fixed in #76785