Start to deduplicate code in qml.

gpt4all-chat/qml/MyComboBox.qml

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+import QtQuick
+import QtQuick.Controls
+import QtQuick.Controls.Basic
+
+ComboBox {
+    font.pixelSize: theme.fontSizeLarge
+    spacing: 0
+    padding: 10
+    Accessible.role: Accessible.ComboBox
+    contentItem: Text {
+        anchors.horizontalCenter: parent.horizontalCenter
+        leftPadding: 10
+        rightPadding: 10
+        text: comboBox.displayText
+        font: comboBox.font
+        color: theme.textColor
+        verticalAlignment: Text.AlignVCenter
+        horizontalAlignment: Text.AlignHCenter
+        elide: Text.ElideRight
+    }
+    delegate: ItemDelegate {
+        width: comboBox.width
+        contentItem: Text {
+            text: modelData
+            color: theme.textColor
+            font: comboBox.font
+            elide: Text.ElideRight
+            verticalAlignment: Text.AlignVCenter
+        }
+        background: Rectangle {
+            color: highlighted ? theme.backgroundLight : theme.backgroundDark
+        }
+        highlighted: comboBox.highlightedIndex === index
+    }
+    popup: Popup {
+        y: comboBox.height - 1
+        width: comboBox.width
+        implicitHeight: contentItem.implicitHeight
+        padding: 0
+
+        contentItem: ListView {
+            clip: true
+            implicitHeight: contentHeight
+            model: comboBox.popup.visible ? comboBox.delegateModel : null
+            currentIndex: comboBox.highlightedIndex
+            ScrollIndicator.vertical: ScrollIndicator { }
+        }
+
+        background: Rectangle {
+            color: theme.backgroundDark
+        }
+    }
+    background: Rectangle {
+        color: theme.backgroundDark
+        border.width: 1
+        border.color: theme.backgroundLightest
+        radius: 10
+    }
+}