21534 [Android Text Input] Make the editing state listenable and allow batch edits  (affects: text input, cla: yes, platform-android, waiting for tree to go green)

21612 Separate mutators for text and selection (affects: desktop, affects: text input, cla: yes, platform-linux, platform-windows, waiting for tree to go green)

21663 Store selection base/extent as size_t (affects: text input, cla: yes, platform-linux, platform-windows)

21682 Add multi-step IME support to TextInputModel (affects: text input, cla: yes, platform-linux, platform-windows)

21685 Make TextInputModel::selection_start/end const (affects: text input, cla: yes, platform-linux, platform-windows)