Migrate to ESLint flat config

Flat config is the new config system used by ESLint 9.
To make the migration easier, they also added
flat config support to ESLint 8.

This commit migrates the various ESLint configs in the repository to use
the new system, **without** upgrading to ESLint 9 yet.

test/.eslintrc

@@ -1,18 +0,0 @@
-{
-  "plugins": ["jasmine"],
-  "extends": ["../.eslintrc", "plugin:jasmine/recommended"],
-  "env": {
-    "node": true,
-    "jasmine": true
-  },
-  "rules": {
-    "jasmine/new-line-before-expect": "off",
-    "jasmine/new-line-between-declarations": "off",
-    "jasmine/no-focused-tests": "error",
-    "jasmine/no-pending-tests": "off",
-    "jasmine/no-spec-dupes": ["error", "branch"],
-    "jasmine/no-suite-dupes": ["error", "branch"],
-    "jasmine/prefer-jasmine-matcher": "off",
-    "jasmine/prefer-toHaveBeenCalledWith": "off"
-  }
-}

test/fuzz/.eslintrc

@@ -1,9 +0,0 @@
-{
-  "extends": [
-    "../.eslintrc"
-  ],
-
-  "rules": {
-    "import/no-unresolved": ["error", { "ignore": [".*/build/image_decoders/.*"] }],
-  },
-}

test/integration/.eslintrc

@@ -1,14 +0,0 @@
-{
-  "extends": [
-    "../.eslintrc"
-  ],
-
-  "rules": {
-    "no-restricted-syntax": ["error",
-      {
-        "selector": "CallExpression[callee.name='waitForTimeout']",
-        "message": "`waitForTimeout` can cause intermittent failures and should not be used (see issue #17656 for replacements).",
-      },
-    ],
-  },
-}

test/unit/.eslintrc

@@ -1,10 +0,0 @@
-{
-  "extends": [
-    "../.eslintrc"
-  ],
-
-  "rules": {
-    // Plugins
-    "import/no-unresolved": ["error", { "ignore": ["pdfjs/"] }],
-  },
-}