Split message content into its own module

This is laying some groundwork for the rich text chatbar.

src/messagecontent/models/linemodel.cpp

@@ -0,0 +1,66 @@
+// SPDX-FileCopyrightText: 2024 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#include "linemodel.h"
+
+LineModel::LineModel(QObject *parent)
+    : QAbstractListModel(parent)
+{
+}
+
+QQuickTextDocument *LineModel::document() const
+{
+    return m_document;
+}
+
+void LineModel::setDocument(QQuickTextDocument *document)
+{
+    if (document == m_document) {
+        return;
+    }
+
+    m_document = document;
+    Q_EMIT documentChanged();
+
+    resetModel();
+}
+
+QVariant LineModel::data(const QModelIndex &index, int role) const
+{
+    if (!index.isValid()) {
+        return {};
+    }
+
+    const auto &row = index.row();
+    if (row < 0 || row > rowCount()) {
+        return {};
+    }
+
+    if (role == LineHeightRole) {
+        auto textDoc = m_document->textDocument();
+        return int(textDoc->documentLayout()->blockBoundingRect(textDoc->findBlockByNumber(row)).height());
+    }
+    return {};
+}
+
+int LineModel::rowCount(const QModelIndex &parent) const
+{
+    Q_UNUSED(parent);
+    if (m_document == nullptr) {
+        return 0;
+    }
+    return m_document->textDocument()->blockCount();
+}
+
+QHash<int, QByteArray> LineModel::roleNames() const
+{
+    return {{LineHeightRole, "docLineHeight"}};
+}
+
+void LineModel::resetModel()
+{
+    beginResetModel();
+    endResetModel();
+}
+
+#include "moc_linemodel.cpp"