PackageJson: Use LiteralUnion for engines field (#1354)

Co-authored-by: Som Shekhar Mukherjee <iamssmkhrj@gmail.com>

Author: derodero24

source/package-json.d.ts

@@ -1,5 +1,5 @@
-import type {LiteralUnion} from './literal-union.d.ts';
 import type {JsonObject, JsonValue} from './json-value.d.ts';
+import type {LiteralUnion} from './literal-union.d.ts';
 
 export namespace PackageJson {
 	/**
@@ -526,7 +526,7 @@ export namespace PackageJson {
 		Engines that this package runs on.
 		*/
 		engines?: {
-			[EngineName in 'npm' | 'node' | string]?: string;
+			[EngineName in LiteralUnion<'npm' | 'node', string>]?: string;
 		};
 
 		/**

test-d/package-json.ts

@@ -49,7 +49,8 @@ expectAssignable<PackageJson.DevEngineDependency>({
 	version: '>= 1.0.0',
 	onFail: 'ignore',
 });
-expectType<Partial<Record<string, string>> | undefined>(packageJson.engines);
+expectType<{[EngineName in LiteralUnion<'npm' | 'node', string>]?: string} | undefined>(packageJson.engines);
+expectAssignable<Partial<Record<string, string>> | undefined>(packageJson.engines);
 expectType<boolean | undefined>(packageJson.engineStrict);
 expectAssignable<
 	| undefined