Axios ES2017 (#4787)

* Added AxiosHeaders class;

* Fixed README.md href;

* Fixed a potential bug with headers normalization;

* Fixed a potential bug with headers normalization;
Refactored accessor building routine;
Refactored default transforms;
Removed `normalizeHeaderName` helper;

* Added `Content-Length` accessor;
Added missed `has` accessor to TS types;

* Added `AxiosTransformStream` class;
Added progress capturing ability for node.js environment;
Added `maxRate` option to limit the data rate in node.js environment;
Refactored event handled by `onUploadProgress` && `onDownloadProgress` listeners in browser environment;
Added progress & data rate tests for the http adapter;
Added response stream aborting test;
Added a manual progress capture test for the browser;
Updated TS types;
Added TS tests;
Refactored request abort logic for the http adapter;
Added ability to abort the response stream;

* Remove `stream/promises` & `timers/promises` modules usage in tests;

* Use `abortcontroller-polyfill`;

* Fixed AxiosTransformStream dead-lock in legacy node versions;
Fixed CancelError emitting in streams;

* Reworked AxiosTransformStream internal logic to optimize memory consumption;
Added throwing an error if the request stream was silently destroying (without error) Refers to #3966;

* Treat the destruction of the request stream as a cancellation of the request;
Fixed tests;

* Emit `progress` event in the next tick;

* Initial refactoring;

* Refactored Mocha tests to use ESM;

* Refactored Karma tests to use rollup preprocessor & ESM;
Replaced grunt with gulp;
Improved dev scripts;
Added Babel for rollup build;

* Added default commonjs package export for Node build;
Added automatic contributors list generator for package.json;

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/adapters/index.js

@@ -0,0 +1,33 @@
+import utils from '../utils.js';
+import httpAdapter from './http.js';
+import xhrAdapter from './xhr.js';
+
+const adapters = {
+  http: httpAdapter,
+  xhr: xhrAdapter
+}
+
+export default {
+  getAdapter: (nameOrAdapter) => {
+    if(utils.isString(nameOrAdapter)){
+      const adapter = adapters[nameOrAdapter];
+
+      if (!nameOrAdapter) {
+        throw Error(
+          utils.hasOwnProp(nameOrAdapter) ?
+            `Adapter '${nameOrAdapter}' is not available in the build` :
+            `Can not resolve adapter '${nameOrAdapter}'`
+        );
+      }
+
+      return adapter
+    }
+
+    if (!utils.isFunction(nameOrAdapter)) {
+      throw new TypeError('adapter is not a function');
+    }
+
+    return nameOrAdapter;
+  },
+  adapters
+}