Migrate deprecated eslint config to to new format

The .eslintrc and .eslintignore formats are deprecated. The new format
uses a single eslint.config.js (or .mjs) file at the top.

eslint.config.mjs

@@ -0,0 +1,98 @@
+import globals from "globals";
+import js from "@eslint/js";
+
+export default [
+    js.configs.recommended,
+    {
+        languageOptions: {
+            ecmaVersion: 2020,
+            sourceType: "module",
+            globals: {
+                ...globals.browser,
+                ...globals.es2020,
+            }
+        },
+        ignores: ["**/xtscancodes.js"],
+        rules: {
+            // Unsafe or confusing stuff that we forbid
+
+            "no-unused-vars": ["error", { "vars": "all",
+                                          "args": "none",
+                                          "ignoreRestSiblings": true,
+                                          "caughtErrors": "none" }],
+            "no-constant-condition": ["error", { "checkLoops": false }],
+            "no-var": "error",
+            "no-useless-constructor": "error",
+            "object-shorthand": ["error", "methods", { "avoidQuotes": true }],
+            "prefer-arrow-callback": "error",
+            "arrow-body-style": ["error", "as-needed", { "requireReturnForObjectLiteral": false } ],
+            "arrow-parens": ["error", "as-needed", { "requireForBlockBody": true }],
+            "arrow-spacing": ["error"],
+            "no-confusing-arrow": ["error", { "allowParens": true }],
+
+            // Enforced coding style
+
+            "brace-style": ["error", "1tbs", { "allowSingleLine": true }],
+            "indent": ["error", 4, { "SwitchCase": 1,
+                                     "VariableDeclarator": "first",
+                                     "FunctionDeclaration": { "parameters": "first" },
+                                     "FunctionExpression": { "parameters": "first" },
+                                     "CallExpression": { "arguments": "first" },
+                                     "ArrayExpression": "first",
+                                     "ObjectExpression": "first",
+                                     "ImportDeclaration": "first",
+                                     "ignoreComments": true }],
+            "comma-spacing": ["error"],
+            "comma-style": ["error"],
+            "curly": ["error", "multi-line"],
+            "func-call-spacing": ["error"],
+            "func-names": ["error"],
+            "func-style": ["error", "declaration", { "allowArrowFunctions": true }],
+            "key-spacing": ["error"],
+            "keyword-spacing": ["error"],
+            "no-trailing-spaces": ["error"],
+            "semi": ["error"],
+            "space-before-blocks": ["error"],
+            "space-before-function-paren": ["error", { "anonymous": "always",
+                                                       "named": "never",
+                                                       "asyncArrow": "always" }],
+            "switch-colon-spacing": ["error"],
+            "camelcase": ["error", { "allow": ["^XK_", "^XF86XK_"] }],
+        }
+    },
+    {
+        files: ["po/po2js", "po/xgettext-html"],
+        languageOptions: {
+            globals: {
+                ...globals.node,
+            }
+        },
+    },
+    {
+        files: ["tests/*"],
+        languageOptions: {
+            globals: {
+                ...globals.node,
+                ...globals.mocha,
+                sinon: false,
+                chai: false,
+            }
+        },
+        rules: {
+            "prefer-arrow-callback": 0,
+            // Too many anonymous callbacks
+            "func-names": "off",
+        },
+    },
+    {
+        files: ["utils/*"],
+        languageOptions: {
+            globals: {
+                ...globals.node,
+            }
+        },
+        rules: {
+            "no-console": 0,
+        },
+    },
+];

package.json

@@ -44,6 +44,7 @@
     "commander": "latest",
     "eslint": "latest",
     "fs-extra": "latest",
+    "globals": "latest",
     "jsdom": "latest",
     "karma": "latest",
     "karma-mocha": "latest",