Migrate from TSLint to ESLint

The former is soft-deprecated and new projects are encouraged to use the
latter; it's also officially endorsed by the TypeScript project.
Rust Analyzer has already migrated and by doing so ourselves before
merging it should make the merger easier.

Author: Xanewok

.eslintrc.json

@@ -0,0 +1,55 @@
+{
+    "env": {
+        "es6": true,
+        "node": true
+    },
+    "extends": [
+        "eslint:recommended",
+        "plugin:@typescript-eslint/recommended",
+        "plugin:@typescript-eslint/recommended-requiring-type-checking",
+        "prettier",
+        "prettier/@typescript-eslint"
+    ],
+    "parser": "@typescript-eslint/parser",
+    "parserOptions": {
+        "project": "tsconfig.json",
+        "sourceType": "module"
+    },
+    "plugins": ["@typescript-eslint"],
+    "rules": {
+        "@typescript-eslint/no-unused-vars": [
+            "error",
+            {
+                "argsIgnorePattern": "^_"
+            }
+        ],
+        "eqeqeq": ["error", "always", { "null": "ignore" }],
+        "prefer-const": "error",
+        "@typescript-eslint/member-delimiter-style": [
+            "error",
+            {
+                "multiline": {
+                    "delimiter": "semi",
+                    "requireLast": true
+                },
+                "singleline": {
+                    "delimiter": "semi",
+                    "requireLast": false
+                }
+            }
+        ],
+        "@typescript-eslint/semi": [
+            "error",
+            "always"
+        ],
+        // TODO: Silenced during TSLint -> ESLint conversion; consider enabling them
+        "no-useless-escape": "off",
+        "@typescript-eslint/no-non-null-assertion": "off",
+        "@typescript-eslint/explicit-module-boundary-types": "off",
+        "@typescript-eslint/no-floating-promises": "off",
+        "@typescript-eslint/restrict-template-expressions": "off",
+        "@typescript-eslint/no-unsafe-member-access": "off",
+        "@typescript-eslint/no-unsafe-assignment": "off",
+        "@typescript-eslint/require-await": "off"
+    }
+}

.vscodeignore

@@ -9,6 +9,7 @@ src/**
 **/.prettierignore
 **/.eslintignore
 prettier.config.js
+.eslintrc.json
 vsc-extension-quickstart.md
 **/tsconfig.json
 **/tslint.json