refactor size calculation

app/lib/utils/text_field_line_count.dart

@@ -0,0 +1,30 @@
+import 'package:flutter/material.dart';
+
+int _getLineCountUsingBoxes(String text, TextStyle style, double maxWidth) {
+  final textSpan = TextSpan(text: text, style: style);
+
+  final textPainter = TextPainter(
+    text: textSpan,
+    textDirection: TextDirection.ltr,
+  );
+
+  textPainter.layout(maxWidth: maxWidth);
+
+  // Select all text
+  final selection = TextSelection(baseOffset: 0, extentOffset: text.length);
+
+  // Each box represents one line
+  final lines = textPainter.getBoxesForSelection(selection);
+  return lines.length;
+}
+
+int? getTextFieldLineCount(GlobalKey key, String text, TextStyle style) {
+  final box = key.currentContext?.findRenderObject();
+  if (box case final RenderBox box) {
+    final width = box.size.width;
+
+    return _getLineCountUsingBoxes(text, style, width);
+  }
+
+  return null;
+}