child_process: add env contents types in JSDoc

Use JSDoc to indicate that the `env` object keys and values must be
strings.

Refs: nodejs#42489 (comment)

PR-URL: nodejs#42494
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

lib/child_process.js

@@ -98,7 +98,7 @@ const MAX_BUFFER = 1024 * 1024;
  * @param {{
  *   cwd?: string;
  *   detached?: boolean;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   execPath?: string;
  *   execArgv?: string[];
  *   gid?: number;
@@ -199,7 +199,7 @@ function normalizeExecArgs(command, options, callback) {
  * @param {string} command
  * @param {{
  *   cmd?: string;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   encoding?: string;
  *   shell?: string;
  *   signal?: AbortSignal;
@@ -253,7 +253,7 @@ ObjectDefineProperty(exec, promisify.custom, {
  * @param {string[]} [args]
  * @param {{
  *   cwd?: string;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   encoding?: string;
  *   timeout?: number;
  *   maxBuffer?: number;
@@ -662,7 +662,7 @@ function abortChildProcess(child, killSignal) {
  * @param {string[]} [args]
  * @param {{
  *   cwd?: string;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   argv0?: string;
  *   stdio?: Array | string;
  *   detached?: boolean;
@@ -735,7 +735,7 @@ function spawn(file, args, options) {
  *   input?: string | Buffer | TypedArray | DataView;
  *   argv0?: string;
  *   stdio?: string | Array;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   uid?: number;
  *   gid?: number;
  *   timeout?: number;
@@ -827,7 +827,7 @@ function checkExecSyncError(ret, args, cmd) {
  *   cwd?: string;
  *   input?: string | Buffer | TypedArray | DataView;
  *   stdio?: string | Array;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   uid?: number;
  *   gid?: number;
  *   timeout?: number;
@@ -864,7 +864,7 @@ function execFileSync(command, args, options) {
  *   cwd?: string;
  *   input?: string | Buffer | TypedArray | DataView;
  *   stdio?: string | Array;
- *   env?: object;
+ *   env?: Record<string, string>;
  *   shell?: string;
  *   uid?: number;
  *   gid?: number;