Upgrade eslint-plugin-matrix-org to 1.2.1

This upgrade came with a number of new lints that needed to be fixed across the code base. Primarily: explicit return types on functions, and explicit visibility modifiers on class members.

package.json

@@ -104,11 +104,13 @@
     "eslint": "^8.14.0",
     "eslint-config-google": "^0.14.0",
     "eslint-config-prettier": "^9.0.0",
+    "eslint-plugin-deprecate": "^0.8.2",
     "eslint-plugin-import": "^2.26.0",
     "eslint-plugin-jsx-a11y": "^6.5.1",
-    "eslint-plugin-matrix-org": "^0.4.0",
+    "eslint-plugin-matrix-org": "^1.2.1",
     "eslint-plugin-react": "^7.29.4",
     "eslint-plugin-react-hooks": "^4.5.0",
+    "eslint-plugin-unicorn": "^48.0.1",
     "i18next-parser": "^6.6.0",
     "identity-obj-proxy": "^3.0.0",
     "jest": "^29.2.2",
@@ -118,6 +120,7 @@
     "sass": "^1.42.1",
     "storybook-builder-vite": "^0.1.12",
     "typescript": "^5.1.6",
+    "typescript-eslint-language-service": "^5.0.5",
     "vite": "^4.2.0",
     "vite-plugin-html-template": "^1.1.0",
     "vite-plugin-svgr": "^3.2.0"