Add deprecation documentation (from Best Practices - SDKv2) (#684)

* added deprecations with some TODOs, some conversion done

* update code examples for all sections but last 2

* added removal docs

* update code examples

* added note about deprecation messages

Author: austinvalle

website/data/plugin-framework-nav-data.json

@@ -179,6 +179,10 @@
     "title": "Debugging",
     "path": "debugging"
   },
+  {
+    "title": "Deprecations, Removals, and Renames",
+    "path": "deprecations"
+  },
   {
     "title": "Migrating from SDK",
     "routes": [