chore(eslint): add provisional flat config

eslint.config.js

@@ -0,0 +1,59 @@
+// FIXME: Sync in customizations from .eslintrc.cjs, then delete that file
+
+import { FlatCompat } from "@eslint/eslintrc";
+import path from "path";
+import { fileURLToPath } from "url";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+const compat = new FlatCompat({
+  baseDirectory: __dirname,
+});
+
+import editorconfig from "eslint-plugin-editorconfig";
+import globals from "globals";
+//import html from "@html-eslint/eslint-plugin";
+//import htmlParser from "@html-eslint/parser";
+import js from "@eslint/js";
+import jsdoc from "eslint-plugin-jsdoc";
+import jsonc from "eslint-plugin-jsonc";
+import jsonSchema from "eslint-plugin-json-schema-validator";
+//import markdown from "eslint-plugin-markdown";
+import prettier from "eslint-plugin-prettier";
+
+export default [
+  js.configs.recommended,
+  ...compat.extends("plugin:@typescript-eslint/strict"),
+  ...compat.extends("plugin:@typescript-eslint/stylistic"),
+  ...compat.plugins("editorconfig"),
+  editorconfig.configs.all,
+  ...compat.config(jsdoc.configs.recommended),
+  ...compat.config(jsonc.configs.base),
+  ...compat.config(jsonSchema.configs.recommended),
+  //...compat.plugins("@html-eslint"),
+  //{
+  //  files: ["**/*.html"],
+  //  languageOptions: {
+  //    parser: htmlParser,
+  //  },
+  //  ...compat.config(html.configs.recommended),
+  //},
+  // NOTE: This contains a circular reference chain
+  //...compat.config(markdown.configs.recommended),
+  ...compat.config(prettier.configs.recommended),
+  {
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+      },
+    },
+    linterOptions: {
+      reportUnusedDisableDirectives: true,
+    },
+    rules: {
+      "@typescript-eslint/no-unused-vars": "warn",
+    },
+  },
+];