chore: add prettier

.prettierignore

@@ -0,0 +1,6 @@
+# Schema files
+specs/**
+docs/public/specs/**
+docs/public/schema/**
+packages/vgplot/spec/dist/mosaic-schema.json
+

.prettierrc.json

@@ -0,0 +1,6 @@
+{
+  "singleQuote": true,
+  "tabWidth": 2,
+  "trailingComma": "none",
+  "printWidth": 120
+}

eslint.config.js

@@ -1,6 +1,7 @@
 import js from '@eslint/js';
 import tseslint from 'typescript-eslint';
 import globals from 'globals';
+import prettier from 'eslint-config-prettier';
 
 /** @type {import('@types/eslint').Linter.Config[]} */
 export default tseslint.config(
@@ -27,5 +28,6 @@ export default tseslint.config(
       "@typescript-eslint/no-this-alias": "warn",
       "@typescript-eslint/ban-ts-comment": "warn"
     },
-  }
+  },
+  prettier
 );