(maint) Add visual ruler for line length (#1359)

Previously it was a little difficult to know when your editing would exceed
the 120 line length limit.  This commit modifies the project settings to add
a simple visual ruler at the 120 char limit.

[skip ci]

.vscode/settings.json

@@ -3,6 +3,8 @@
     "editor.tabSize": 4,
     "editor.insertSpaces": true,
     "files.trimTrailingWhitespace": true,
+    // Add a visual ruler for the typescript linting line length
+    "editor.rulers": [120],
 
     "search.exclude": {
         "**/node_modules": true,
@@ -13,4 +15,4 @@
 
     // Lock the TypeScript SDK path to the version we use
     "typescript.tsdk": "./node_modules/typescript/lib"
-}
+}