SelectableRegionState currently mixes in TextSelectionDelegate in order to receive text selection toolbar functionality, however, this functionality is being remove from TextSelectionDelegate in #107193. After the deprecations in that PR are removed, it should be possible to remove TextSelectionDelegate from SelectableRegionState altogether.

Why remove TextSelectionDelegate?

TextSelectionDelegate provides functionality that is related to editing text and which SelectableRegion doesn't use (example). Text selection should be separate from text editing.

CC @chunhtai