[Chat] - Create a bottom mounted floating chat sheet (Resolves #2803)

super_editor/.run/Example - Chat - Bottom Mounted Sheet.run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Example - Chat - Bottom Mounted Sheet" type="FlutterRunConfigurationType" factoryName="Flutter">
+    <option name="filePath" value="$PROJECT_DIR$/example_chat/lib/main_bottom_mounted_sheet.dart" />
+    <method v="2" />
+  </configuration>
+</component>

super_editor/.run/Example - Chat - Floating Editor (Configured).run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Example - Chat - Floating Editor (Configured)" type="FlutterRunConfigurationType" factoryName="Flutter">
+    <option name="filePath" value="$PROJECT_DIR$/example_chat/lib/main_configured_floating_chat_page.dart" />
+    <method v="2" />
+  </configuration>
+</component>

super_editor/.run/Example - Chat - Floating Editor (Default).run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Example - Chat - Floating Editor (Default)" type="FlutterRunConfigurationType" factoryName="Flutter">
+    <option name="filePath" value="$PROJECT_DIR$/example_chat/lib/main_default_floating_chat_page.dart" />
+    <method v="2" />
+  </configuration>
+</component>

super_editor/example_chat/lib/floating_chat_editor_demo/fake_chat_thread.dart

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+import 'package:flutter/material.dart';
+
+/// A simulated chat conversation thread, which is simulated as a bottom-aligned
+/// list of tiles.
+class FakeChatThread extends StatelessWidget {
+  const FakeChatThread({super.key, this.scrollPadding = EdgeInsets.zero});
+
+  final EdgeInsets scrollPadding;
+
+  @override
+  Widget build(BuildContext context) {
+    return ListView.builder(
+      padding: scrollPadding,
+      reverse: true,
+      // ^ The list starts at the bottom and grows upward. This is how
+      //   we should layout chat conversations where the most recent
+      //   message appears at the bottom, and you want to retain the
+      //   scroll offset near the newest messages, not the oldest.
+      itemBuilder: (context, index) {
+        if (index == 8) {
+          // Arbitrarily placed text field to test moving focus between a non-editor
+          // and the editor.
+          return TextField(
+            decoration: InputDecoration(
+              hintText: "Content text field...",
+            ),
+          );
+        }
+
+        return Padding(
+          padding: const EdgeInsets.symmetric(vertical: 4),
+          child: Material(
+            color: Colors.white.withValues(alpha: 0.5),
+            child: ListTile(
+              title: Text("This is item $index"),
+              subtitle: Text("This is a subtitle for $index"),
+            ),
+          ),
+        );
+      },
+    );
+  }
+}