[p-map] introduce typings (#18544)

* [p-map] introduce typings

* [p-map] simplify according to review discussion

types/p-map/index.d.ts

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+// Type definitions for p-map 1.1
+// Project: https://github.com/sindresorhus/p-map#readme
+// Definitions by: BendingBender <https://github.com/BendingBender>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.3
+
+export = pMap;
+
+declare function pMap<T = any, M = T>(input: Iterable<Input<T>>, mapper: Mapper<T, M>, options?: pMap.Options): Promise<M[]>;
+
+type Input<T> = Promise<T> | PromiseLike<T> | T;
+type Mapper<T, R> = (el: T, index: number) => Promise<R> | R;
+
+declare namespace pMap {
+    interface Options {
+        concurrency?: number;
+    }
+}

types/p-map/p-map-tests.ts

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+import pMap = require('p-map');
+
+const sites = [
+    Promise.resolve('sindresorhus'),
+    true,
+    1
+];
+
+const mapper = (el: number | string | boolean) => Promise.resolve(1);
+
+let num: number;
+pMap(sites, mapper, {concurrency: 2}).then(result => {
+    num = result[3];
+});
+
+pMap(sites, mapper).then(result => {
+    num = result[3];
+});

types/p-map/tsconfig.json

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+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": true,
+        "baseUrl": "../",
+        "typeRoots": [
+            "../"
+        ],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "p-map-tests.ts"
+    ]
+}

types/p-map/tslint.json

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+{ "extends": "dtslint/dt.json" }