Add ability to provide generic for the internal type of the TextAnnotator

[oleksandr-danylchenko]

Current State

Currently, the TextAnnotator allows to provide a generic only for the external type:

text-annotator-js/packages/text-annotator/src/TextAnnotator.ts

Line 13 in 3f587dd

export interface TextAnnotator<T extends unknown = TextAnnotation> extends Annotator<TextAnnotation, T> {

And everywhere in the following code, only the TextAnnotation is hard-binded

Issue

When a user (me 😅) wants to extend the TextAnnotator with some plugin that might mutate the TextAnnotation with additional properties - I'm pretty much out of luck... Because the TextAnnotator, TextAnnotatorState, are strictly bound to the R6O TextAnnotation type.

The one option is to define the .d.ts file and override the TextAnnotation there. But it creates inconvenient indirectness and maintainers will have questions...

However, another better alternative is to make the TextAnnotator look something like this:

export interface TextAnnotator<I extends TextAnnotation = TextAnnotation, E extends unknown = TextAnnotation> extends Annotator<I, E> {

  element: HTMLElement;

  // Returns true if successful (or false if the annotation is not currently rendered)
  scrollIntoView(annotation: I): boolean;

  state: TextAnnotatorState<I>;

}

In that way - lib consumers can safely describe the extended internal types. And then simply use the typed useAnnotator and useAnnotatorStore hooks

[oleksandr-danylchenko]

I also tried following the RecogitoTEIAnnotator example:

text-annotator-js/packages/extension-tei/src/TEIPlugin.ts

Lines 34 to 36 in 3a70b9e

	export interface RecogitoTEIAnnotator<T extends unknown = TEIAnnotation> extends Annotator<TEIAnnotation, T> { }
	export const TEIPlugin = (anno: TextAnnotator): RecogitoTEIAnnotator => {

But I think that using the extends Annotator for the plugin that works with the TextAnnotator won't be a precise type depiction. Because the latter adds new props (element, scrollIntoView, etc.) and overrides some of the lifecycle methods of the store (addAnnotation, getAnnotationBounds, etc.). Unfortunately, the extended Annotator won't have any of those...
Instead, I would like to be able to use the TextAnnotator type directly with a slightly updated internal model. Which cannot be done at the moment 🤷🏻‍♂️