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>

tool/flutter_ci_script_beta.sh

@@ -39,6 +39,7 @@ declare -ar PROJECT_NAMES=(
     "platform_view_swift"
     "provider_counter"
     "provider_shopper"
+    "simplistic_editor"
     # TODO(domesticmouse): Re-enable once Dart 2.17 is stable
     # "testing_app"
     "veggieseasons"

tool/flutter_ci_script_stable.sh

@@ -35,6 +35,8 @@ declare -ar PROJECT_NAMES=(
     "platform_view_swift"
     "provider_counter"
     "provider_shopper"
+    # TODO: Re-enable once Dart 2.17 is stable
+    # "simplistic_editor"
     "testing_app"
     "veggieseasons"
 )