Show the selection's commands beside the cursor after a click

After a click that selects something on a folio, a small row of commands
appears just above and to the right of the cursor, as the SolidWorks
context toolbar does. It fades as the mouse moves away and is gone past
200 pixels; a click elsewhere, the wheel, a key press or an emptied
selection hide it too. Clicking a command leaves it up, so rotate can be
clicked again.

The commands are the shortcut bar's for that selection -- elements or
conductors -- at most eight, so customising the bar customises this as
well. It is a child of the view's viewport, never a window, and never
takes the focus.

It is not shown after a drag (moving items, a rubber band), while
placing or drawing (Diagram::eventInterfaceIsRunning()), on
a read-only folio, or when switched off with the new General option
"Afficher les commandes près de la sélection" (diagrameditor/
context_toolbar, on by default).

ShortcutBarSettings::contextFor() now decides the context for both the
bar and this toolbar.

Discussion #1033.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G2d2Zi8BfrYRPX88zhaoFG
(cherry picked from commit 78f3c1a2bc5c3cf1f7beae4bd60aefec20847d6d)

sources/shortcutbarsettings.cpp

@@ -17,9 +17,11 @@
 */
 #include "shortcutbarsettings.h"
 
+#include "qetgraphicsitem/conductor.h"
 #include "shortcutmanager.h"
 
 #include <QCoreApplication>
+#include <algorithm>
 #include <QSettings>
 
 namespace {
@@ -46,6 +48,22 @@ QList<ShortcutBarSettings::Context> ShortcutBarSettings::contexts()
 	return {Canvas, Selection, Conductor};
 }
 
+/**
+	@return the context for @a selection: Canvas when empty, Conductor when
+	it holds only conductors, Selection otherwise
+*/
+ShortcutBarSettings::Context ShortcutBarSettings::contextFor(
+		const QList<QGraphicsItem *> &selection)
+{
+	if (selection.isEmpty()) {
+		return Canvas;
+	}
+	const bool only_conductors = std::all_of(
+		selection.cbegin(), selection.cend(),
+		[](QGraphicsItem *item) { return item->type() == Conductor::Type; });
+	return only_conductors ? Conductor : Selection;
+}
+
 /**
 	@return the name of @a context, for the configuration page
 */