feat(ui): selectionActionsIcon on the toolbar seam, simpler default wand (#1575)

AnnotationToolbar.selectionActionsIcon lets a host supply the glyph on the selectionActions button, forwarded by Viewer (both toolbars) and HtmlViewer; absent means the package's own wand, now one thick diagonal with a single star. Rides in the unpublished ui 0.43.1; no version bump.