Add magnifier to text selection & better platform-specific behavior o…

…f text selection (#198)

* New contextual menu implementation (Strongly inspired by Flutter)

* Bring into view upon selection

* Spell check functional

* Handle dragging the base handle that makes it the extent on Apple platforms

* Apply suggested changes

* Show magnifier on long tap with collapsed selection (mobile)

* Add spell check configuration to example

packages/fleather/example/lib/main.dart

@@ -84,6 +84,11 @@ class _HomePageState extends State<HomePage> {
                     onLaunchUrl: _launchUrl,
                     maxContentWidth: 800,
                     embedBuilder: _embedBuilder,
+                    spellCheckConfiguration: SpellCheckConfiguration(
+                        spellCheckService: DefaultSpellCheckService(),
+                        misspelledSelectionColor: Colors.red,
+                        misspelledTextStyle:
+                            DefaultTextStyle.of(context).style),
                   ),
                 ),
               ],

packages/fleather/lib/src/rendering/editable_text_line.dart

@@ -52,6 +52,7 @@ class RenderEditableTextLine extends RenderEditableBox {
   //
 
   InlineCodeThemeData _inlineCodeTheme;
+
   set inlineCodeTheme(InlineCodeThemeData theme) {
     if (_inlineCodeTheme == theme) return;
     _inlineCodeTheme = theme;
@@ -332,6 +333,12 @@ class RenderEditableTextLine extends RenderEditableBox {
     final lineDy = caret.translate(0.0, 0.5 * preferredLineHeight(position)).dy;
     final boxes = getBoxesForSelection(
         TextSelection(baseOffset: 0, extentOffset: node.length - 1));
+
+    // If document is empty, boxes will be empty
+    // TextPainter (RenderParagraphProxy -> RenderParagraph) returns no boxes
+    // when it has not text
+    if (boxes.isEmpty) return const TextRange.collapsed(0);
+
     final lineBoxes = boxes
         .where((element) => element.top < lineDy && element.bottom > lineDy)
         .toList(growable: false);

packages/fleather/lib/src/rendering/editor.dart

@@ -366,7 +366,6 @@ class RenderEditor extends RenderEditableContainerBox
   @override
   List<TextSelectionPoint> getEndpointsForSelection(TextSelection selection) {
     // _layoutText(minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
-
     if (selection.isCollapsed) {
       final child = childAtPosition(selection.extent);
       final localPosition =