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/web/manifest.json

@@ -0,0 +1,35 @@
+{
+    "name": "simplistic_editor",
+    "short_name": "simplistic_editor",
+    "start_url": ".",
+    "display": "standalone",
+    "background_color": "#0175C2",
+    "theme_color": "#0175C2",
+    "description": "A new Flutter project.",
+    "orientation": "portrait-primary",
+    "prefer_related_applications": false,
+    "icons": [
+        {
+            "src": "icons/Icon-192.png",
+            "sizes": "192x192",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        },
+        {
+            "src": "icons/Icon-maskable-192.png",
+            "sizes": "192x192",
+            "type": "image/png",
+            "purpose": "maskable"
+        },
+        {
+            "src": "icons/Icon-maskable-512.png",
+            "sizes": "512x512",
+            "type": "image/png",
+            "purpose": "maskable"
+        }
+    ]
+}