Flip Elsewhen between Fahrenheit and Celsius with Alt+T (#13450)

* Flip Elsewhen between Fahrenheit and Celsius with Shift+T

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

* Flip Elsewhen's temperature units with Alt+T instead of Shift+T

PanelKeyCatcher's textKey now carries the held modifiers, which is how the
panel tells Alt+T from T. Existing handlers take only the text and are
unaffected.

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/shell.d/panel-key-catcher/qml/tst_modifiers.qml

@@ -0,0 +1,45 @@
+import QtQuick
+import QtTest
+import "../../../../shell/Ui"
+
+// Text keys carry their modifiers, so a panel can tell Alt+T from T.
+Item {
+  id: root
+  width: 100
+  height: 100
+
+  property string lastText: ""
+  property int lastModifiers: -1
+
+  PanelKeyCatcher {
+    id: catcher
+    anchors.fill: parent
+    onTextKey: function(text, modifiers) {
+      root.lastText = text
+      root.lastModifiers = modifiers
+    }
+  }
+
+  TestCase {
+    name: "PanelKeyCatcherModifiers"
+    when: windowShown
+
+    function init() {
+      catcher.forceActiveFocus()
+      root.lastText = ""
+      root.lastModifiers = -1
+    }
+
+    function test_plainLetterHasNoModifiers() {
+      keyClick(Qt.Key_T)
+      compare(root.lastText, "t")
+      compare(root.lastModifiers & Qt.AltModifier, 0)
+    }
+
+    function test_altLetterCarriesAlt() {
+      keyClick(Qt.Key_T, Qt.AltModifier)
+      compare(root.lastText.toLowerCase(), "t")
+      verify(root.lastModifiers & Qt.AltModifier)
+    }
+  }
+}