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>

test/specs/helpers/toFormData.spec.js

@@ -1,15 +1,15 @@
-var toFormData = require('../../../lib/helpers/toFormData');
+import toFormData from '../../../lib/helpers/toFormData';
 
 describe('toFormData', function () {
   it('should convert nested data object to FormData with dots option enabled', function () {
-    var o = {
+    const o = {
       val: 123,
       nested: {
         arr: ['hello', 'world']
       }
     };
 
-    var form = toFormData(o, null, {dots: true});
+    const form = toFormData(o, null, {dots: true});
     expect(form instanceof FormData).toEqual(true);
     expect(Array.from(form.keys()).length).toEqual(3);
     expect(form.get('val')).toEqual('123');
@@ -17,13 +17,13 @@ describe('toFormData', function () {
   });
 
   it('should respect metaTokens option', function () {
-    var data = {
+    const data = {
       'obj{}': {x: 1, y: 2}
     };
 
-    var str = JSON.stringify(data['obj{}']);
+    const str = JSON.stringify(data['obj{}']);
 
-    var form = toFormData(data, null, {metaTokens: false});
+    const form = toFormData(data, null, {metaTokens: false});
 
     expect(Array.from(form.keys()).length).toEqual(1);
     expect(form.getAll('obj')).toEqual([str]);
@@ -31,12 +31,12 @@ describe('toFormData', function () {
 
   describe('Flat arrays serialization', function () {
     it('should include full indexes when the `indexes` option is set to true', function () {
-      var data = {
+      const data = {
         arr: [1, 2, 3],
         arr2: [1, [2], 3]
       };
 
-      var form = toFormData(data, null, {indexes: true});
+      const form = toFormData(data, null, {indexes: true});
 
       expect(Array.from(form.keys()).length).toEqual(6);
 
@@ -50,12 +50,12 @@ describe('toFormData', function () {
     });
 
     it('should include brackets only when the `indexes` option is set to false', function () {
-      var data = {
+      const data = {
         arr: [1, 2, 3],
         arr2: [1, [2], 3]
       };
 
-      var form = toFormData(data, null, {indexes: false});
+      const form = toFormData(data, null, {indexes: false});
 
       expect(Array.from(form.keys()).length).toEqual(6);
 
@@ -67,12 +67,12 @@ describe('toFormData', function () {
     });
 
     it('should omit brackets when the `indexes` option is set to null', function () {
-      var data = {
+      const data = {
         arr: [1, 2, 3],
         arr2: [1, [2], 3]
       };
 
-      var form = toFormData(data, null, {indexes: null});
+      const form = toFormData(data, null, {indexes: null});
 
       expect(Array.from(form.keys()).length).toEqual(6);
 
@@ -85,14 +85,14 @@ describe('toFormData', function () {
   });
 
   it('should convert nested data object to FormData', function () {
-    var o = {
+    const o = {
       val: 123,
       nested: {
         arr: ['hello', 'world']
       }
     };
 
-    var form = toFormData(o);
+    const form = toFormData(o);
     expect(form instanceof FormData).toEqual(true);
     expect(Array.from(form.keys()).length).toEqual(3);
     expect(form.get('val')).toEqual('123');
@@ -100,24 +100,24 @@ describe('toFormData', function () {
   });
 
   it('should append value whose key ends with [] as separate values with the same key', function () {
-    var data = {
+    const data = {
       'arr[]': [1, 2, 3]
     };
 
-    var form = toFormData(data);
+    const form = toFormData(data);
 
     expect(Array.from(form.keys()).length).toEqual(3);
     expect(form.getAll('arr[]')).toEqual(['1', '2', '3']);
   });
 
   it('should append value whose key ends with {} as a JSON string', function () {
-    var data = {
+    const data = {
       'obj{}': {x: 1, y: 2}
     };
 
-    var str = JSON.stringify(data['obj{}']);
+    const str = JSON.stringify(data['obj{}']);
 
-    var form = toFormData(data);
+    const form = toFormData(data);
 
     expect(Array.from(form.keys()).length).toEqual(1);
     expect(form.getAll('obj{}')).toEqual([str]);