Overhaul linting, formatting, and testing infrastructure

.editorconfig

@@ -5,6 +5,7 @@ charset = utf-8
 indent_style = space
 indent_size = 4
 insert_final_newline = true
+trim_trailing_whitespace = true
 
 [*.{json,yaml,yml,code-workspace}]
 indent_size = 2

.prettierignore

@@ -0,0 +1,3 @@
+dist/
+modules/
+out/

.vscode-test.mjs

@@ -0,0 +1,20 @@
+import { defineConfig } from "@vscode/test-cli";
+import os from "os";
+import path from "path";
+
+export default defineConfig({
+    files: "test/**/*.test.ts",
+    // The default user data directory had too many characters for the IPC connection on macOS in CI.
+    launchArgs: [
+        "--profile-temp",
+        "--user-data-dir",
+        path.join(os.tmpdir(), "vscode-user-data"),
+    ],
+    workspaceFolder: "test/TestEnvironment.code-workspace",
+    mocha: {
+        ui: "bdd", // describe, it, etc.
+        require: ["esbuild-register"], // transpile TypeScript on-the-fly
+        slow: 2000, // 2 seconds for slow test
+        timeout: 60 * 1000, // 10 minutes to allow for debugging
+    },
+});

eslint.config.mjs

@@ -0,0 +1,49 @@
+import eslint from "@eslint/js";
+import eslintConfigPrettier from "eslint-config-prettier/flat";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+    eslint.configs.recommended,
+    tseslint.configs.strictTypeChecked,
+    tseslint.configs.stylisticTypeChecked,
+    eslintConfigPrettier,
+    {
+        languageOptions: {
+            parserOptions: {
+                projectService: true,
+                tsconfigRootDir: import.meta.dirname,
+            },
+        },
+        rules: {
+            "@typescript-eslint/explicit-function-return-type": "error",
+            "@typescript-eslint/no-empty-object-type": "off",
+            "@typescript-eslint/no-floating-promises": [
+                "error",
+                {
+                    ignoreVoid: true,
+                },
+            ],
+            "@typescript-eslint/no-non-null-assertion": "off",
+            "@typescript-eslint/no-require-imports": "off",
+            "@typescript-eslint/no-unused-vars": [
+                "error",
+                {
+                    argsIgnorePattern: "^_",
+                },
+            ],
+            "@typescript-eslint/no-unsafe-argument": "off",
+            "@typescript-eslint/no-unsafe-assignment": "off",
+            "@typescript-eslint/no-unsafe-call": "off",
+            "@typescript-eslint/no-unsafe-member-access": "off",
+            "@typescript-eslint/no-unsafe-return": "off",
+            "@typescript-eslint/restrict-template-expressions": "off",
+            "@typescript-eslint/prefer-nullish-coalescing": [
+                "error",
+                {
+                    ignoreConditionalTests: true,
+                    ignoreMixedLogicalExpressions: true,
+                },
+            ],
+        },
+    },
+);