Add simplistic editor to samples to showcase TextEditingDeltas (#1217)

* Add simplistic editor to samples

* Toggle styles fix

* update name

* Add to CI and dependabot

* update minimum dart sdk

* fix pubspec

* update README

* Update README

* Add shift + arrow key selection and copy/paste keyboard actions

* Update README.md

* copy edits to readme

includes a sentence in each layer description whose accuracy I still need to verify

* update pubspec

* update pubspec.lock

* Fix bug with disabling expansion of replacement when cursor is at edge of replacement

Co-authored-by: Renzo Olivares <roliv@google.com>
Co-authored-by: Craig Labenz <craig.labenz@gmail.com>

simplistic_editor/.metadata

@@ -0,0 +1,36 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled.
+
+version:
+  revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+  channel: master
+
+project_type: app
+
+# Tracks metadata for the flutter migrate command
+migration:
+  platforms:
+    - platform: root
+      create_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+      base_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+    - platform: linux
+      create_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+      base_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+    - platform: macos
+      create_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+      base_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+    - platform: windows
+      create_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+      base_revision: 14a9b4a7512c9bc40d0417672a87276bd48df2ad
+
+  # User provided section
+
+  # List of Local paths (relative to this file) that should be
+  # ignored by the migrate tool.
+  #
+  # Files that are not part of the templates will be ignored by default.
+  unmanaged_files:
+    - 'lib/main.dart'
+    - 'ios/Runner.xcodeproj/project.pbxproj'