Switch to eslint flat config (#57684)

src/.eslintrc.json

@@ -1,49 +0,0 @@
-{
-    "extends": "../.eslintrc.json",
-    "parserOptions": {
-        "tsconfigRootDir": "src",
-        "project": "./tsconfig-eslint.json"
-    },
-    "rules": {
-        "@typescript-eslint/no-unnecessary-type-assertion": "error",
-        "no-restricted-globals": [
-            "error",
-            { "name": "setTimeout" },
-            { "name": "clearTimeout" },
-            { "name": "setInterval" },
-            { "name": "clearInterval" },
-            { "name": "setImmediate" },
-            { "name": "clearImmediate" },
-            { "name": "performance" }
-        ]
-    },
-    "overrides": [
-        {
-            "files": ["lib/*.d.ts"],
-            "rules": {
-                "@typescript-eslint/interface-name-prefix": "off",
-                "@typescript-eslint/prefer-function-type": "off",
-                "@typescript-eslint/unified-signatures": "off",
-
-                // scripts/eslint/rules
-                "local/no-keywords": "off",
-
-                // eslint
-                "no-var": "off",
-                "no-restricted-globals": "off"
-            }
-        },
-        {
-            "files": ["lib/es2019.array.d.ts"],
-            "rules": {
-                "@typescript-eslint/array-type": "off"
-            }
-        },
-        {
-            "files": ["debug/**", "harness/**", "testRunner/**"],
-            "rules": {
-                "no-restricted-globals": "off"
-            }
-        }
-    ]
-}