refactor(core/form/inputs): add prop __unstable_textElementFocus

Added a untable prop for BlockAnnotationProps to know if the retlated editor text element has focus.
This differs from form focus on the annotation object itself (markDef).

packages/sanity/src/core/form/types/blockProps.ts

@@ -56,6 +56,7 @@ export interface BlockListItemProps {
 export interface BlockAnnotationProps {
   __unstable_boundaryElement?: HTMLElement // Boundary element for the annotation, typically a scroll container
   __unstable_referenceElement?: HTMLElement // Reference element representing the annotation in the DOM
+  __unstable_textElementFocus?: boolean // Wether the related text element (in the editor) has selection focus. Differs from form state focus.
   children?: ReactNode | undefined
   focused: boolean // Whether the annotation data object has form focus
   markers: PortableTextMarker[]