Add ESLint configuration files

.eslintignore

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+_locales
+audit
+icons
+modules/*
+!modules/internal
+resources

.eslintrc

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+{
+  "env": {
+    "browser": true,
+    "es6": true,
+    "webextensions": true
+  },
+  "extends": "eslint:recommended",
+  "globals": {
+    "files": true,
+    "helpers": true,
+    "HOST_PREFIX": true,
+    "HOST_SUFFIX": true,
+    "HTTP_EXPRESSION": true,
+    "interceptor": true,
+    "MAPPING_FILE_EXPRESSION": true,
+    "mappings": true,
+    "REQUEST_BLOCKING": true,
+    "REQUEST_HEADERS": true,
+    "requestAnalyzer": true,
+    "resources": true,
+    "stateManager": true,
+    "VALUE_SEPARATOR": true,
+    "VERSION_EXPRESSION": true,
+    "VERSION_PLACEHOLDER": true,
+    "WEB_DOMAIN_EXPRESSION": true,
+    "WEB_PREFIX_LENGTH": true,
+    "WEB_PREFIX_VALUE": true
+  },
+  "overrides": {
+    "files": [
+      "core/constants.js",
+      "core/files.js",
+      "core/mappings.js",
+      "core/resources.js"
+    ],
+    "rules": {
+      "no-unused-vars": "off"
+    }
+  },
+  "rules": {
+    "array-bracket-newline": "error",
+    "array-bracket-spacing": "error",
+    "arrow-body-style": "error",
+    "arrow-parens": "error",
+    "arrow-spacing": "error",
+    "block-spacing": "error",
+    "brace-style": "error",
+    "camelcase": "error",
+    "comma-spacing": "error",
+    "comma-style": "error",
+    "computed-property-spacing": "error",
+    "consistent-this": "error",
+    "curly": "error",
+    "eol-last": "error",
+    "eqeqeq": "error",
+    "func-call-spacing": "error",
+    "function-paren-newline": "error",
+    "generator-star-spacing": "error",
+    "indent": [
+      "error",
+      4
+    ],
+    "key-spacing": "error",
+    "keyword-spacing": "error",
+    "linebreak-style": [
+      "error",
+      "unix"
+    ],
+    "new-cap": "error",
+    "new-parens": "error",
+    "no-array-constructor": "error",
+    "no-bitwise": "error",
+    "no-confusing-arrow": "error",
+    "no-continue": "error",
+    "no-duplicate-imports": "error",
+    "no-eval": "error",
+    "no-extend-native": "error",
+    "no-implicit-coercion": "error",
+    "no-implied-eval": "error",
+    "no-invalid-this": "error",
+    "no-iterator": "error",
+    "no-label-var": "error",
+    "no-labels": "error",
+    "no-lone-blocks": "error",
+    "no-loop-func": "error",
+    "no-multi-spaces": "error",
+    "no-multi-str": "error",
+    "no-multiple-empty-lines": [
+      "error", {
+        "max": 1,
+        "maxEOF": 1,
+        "maxBOF": 0
+      }
+    ],
+    "max-len": [
+      "error", {
+        "code": 120
+      }
+    ],
+    "no-negated-condition": "error",
+    "no-new": "error",
+    "no-new-func": "error",
+    "no-new-object": "error",
+    "no-new-wrappers": "error",
+    "no-octal-escape": "error",
+    "no-proto": "error",
+    "no-return-assign": "error",
+    "no-return-await": "error",
+    "no-script-url": "error",
+    "no-self-compare": "error",
+    "no-sequences": "error",
+    "no-shadow-restricted-names": "error",
+    "no-tabs": "error",
+    "no-ternary": "error",
+    "no-throw-literal": "error",
+    "no-trailing-spaces": "error",
+    "no-undef-init": "error",
+    "no-unmodified-loop-condition": "error",
+    "no-unused-expressions": "error",
+    "no-use-before-define": "error",
+    "no-useless-call": "error",
+    "no-useless-concat": "error",
+    "no-useless-constructor": "error",
+    "no-useless-rename": "error",
+    "no-useless-return": "error",
+    "no-void": "error",
+    "no-warning-comments": "warn",
+    "no-whitespace-before-property": "error",
+    "no-with": "error",
+    "object-curly-spacing": "error",
+    "object-shorthand": [
+      "error",
+      "consistent-as-needed"
+    ],
+    "operator-assignment": "error",
+    "operator-linebreak": "error",
+    "prefer-numeric-literals": "error",
+    "prefer-promise-reject-errors": "error",
+    "quote-props": "error",
+    "prefer-rest-params": "error",
+    "prefer-spread": "error",
+    "prefer-template": "error",
+    "quotes": [
+      "error",
+      "single"
+    ],
+    "rest-spread-spacing": "error",
+    "require-await": "error",
+    "semi": "error",
+    "semi-spacing": "error",
+    "semi-style": "error",
+    "space-before-blocks": "error",
+    "space-before-function-paren": "error",
+    "space-in-parens": "error",
+    "space-infix-ops": "error",
+    "space-unary-ops": "error",
+    "spaced-comment": "error",
+    "strict": [
+      "error",
+      "global"
+    ],
+    "switch-colon-spacing": "error",
+    "symbol-description": "error",
+    "template-curly-spacing": "error",
+    "template-tag-spacing": "error",
+    "unicode-bom": "error",
+    "vars-on-top": "error",
+    "wrap-regex": "error",
+    "yield-star-spacing": "error",
+    "yoda": "error"
+  }
+}

audit/.eslintrc

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+{
+  "env": {
+    "es6": true,
+    "node": true
+  },
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "sourceType": "module"
+  },
+  "rules": {
+    "indent": [
+      "error",
+      4
+    ],
+    "linebreak-style": [
+      "error",
+      "unix"
+    ],
+    "no-console": "off",
+    "no-use-before-define": "error",
+    "operator-assignment": "error",
+    "prefer-template": "error",
+    "quotes": [
+      "error",
+      "single"
+    ],
+    "semi": [
+      "error",
+      "always"
+    ]
+  }
+}