Full keyboard mode, Ctrl/Alt/Super, dead keys, shift levels

- Full (iPad Pro) mode: every typing key from the keymap, number row,
  tab, caps lock, ctrl/super/alt; shifted symbol shown above and flickable
- Dead keys compose with the locale's XKB compose table
- Ctrl/Alt/Super stick like shift and turn keys into shortcuts; a tapped
  or held shift joins shortcuts and non-text keys, auto-shift and caps
  lock don't
- Auto-capitalization and caps lock only capitalize letters; the user's
  shift picks the keymap's shifted level
- Mode switch in settings keeps key size by resizing the window

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/layout/KeymapKeys.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <QList>
+#include <QString>
+
+struct xkb_keymap;
+
+// One typing key of a keymap layout, at its two shift levels. A level is
+// either text or a dead key (then `text` is its spacing accent, for labels).
+struct KeymapKey {
+    enum class Position { Regular, Backslash, LessGreater }; // BKSL, LSGT: not on every keyboard
+
+    Position position = Position::Regular;
+    QString lower;
+    QString upper;
+    quint32 deadLower = 0; // dead keysym, 0 if the level types text
+    quint32 deadUpper = 0;
+
+    bool isLetter() const;
+};
+
+// The typing keys one layout of an XKB keymap has on a physical keyboard,
+// in its four rows: 0 number row (TLDE, AE01–AE12), 1 top (AD01–AD12, BKSL),
+// 2 home (AC01–AC11), 3 bottom (LSGT, AB01–AB10). Keys that type nothing on
+// either level are left out.
+struct KeymapKeys {
+    QString name; // e.g. "Slovak"
+    QList<QList<KeymapKey>> rows;
+};
+
+KeymapKeys readKeymapKeys(xkb_keymap *keymap, quint32 layoutIndex);
+
+// What a dead key shows and types when nothing composes: ´ for dead_acute.
+QString deadKeyText(quint32 keysym);