Fix: allow / in addition to %2f in the url for scope checks (#4367)

**Summary**

Fixes #4366. NPM registry encodes the `/` in scoped package names for meta look ups but not for tarball download URLs so Yarn was not sending authentication headers for the tarball downloads breaking scoped packages. This patch fixes it.

**Test plan**

Updated tests.

__tests__/registries/npm-registry.js

@@ -254,7 +254,7 @@ describe('isRequestToRegistry functional test', () => {
 const packageIdents = [
   ['normal', ''],
   ['@scopedNoPkg', ''],
-  ['@scoped/notescaped', ''],
+  ['@scoped/notescaped', '@scoped'],
   ['not@scope/pkg', ''],
   ['@scope?query=true', ''],
   ['@scope%2fpkg', '@scope'],
@@ -263,13 +263,15 @@ const packageIdents = [
   ['@scope%2fpkg%2f1.2.3', '@scope'],
   ['http://foo.bar:80/normal', ''],
   ['http://foo.bar:80/@scopedNoPkg', ''],
-  ['http://foo.bar:80/@scoped/notescaped', ''],
+  ['http://foo.bar:80/@scoped/notescaped', '@scoped'],
+  ['http://foo.bar:80/@scoped/notescaped/download/@scoped/notescaped-1.0.0.tgz', '@scoped'],
   ['http://foo.bar:80/not@scope/pkg', ''],
   ['http://foo.bar:80/@scope?query=true', ''],
   ['http://foo.bar:80/@scope%2fpkg', '@scope'],
   ['http://foo.bar:80/@scope%2fpkg%2fext', '@scope'],
   ['http://foo.bar:80/@scope%2fpkg?query=true', '@scope'],
   ['http://foo.bar:80/@scope%2fpkg%2f1.2.3', '@scope'],
+  ['http://foo.bar:80/@scope%2fpkg/download/@scope%2fpkg-1.0.0.tgz', '@scope'],
 ];
 
 describe('isScopedPackage functional test', () => {

src/registries/npm-registry.js

@@ -27,8 +27,11 @@ export const SCOPE_SEPARATOR = '%2f';
 // All scoped package names are of the format `@scope%2fpkg` from the use of NpmRegistry.escapeName
 // `(?:^|\/)` Match either the start of the string or a `/` but don't capture
 // `[^\/?]+?` Match any character that is not '/' or '?' and capture, up until the first occurance of:
-// `%2f` Match SCOPE_SEPARATOR, the escaped '/', and don't capture
-const SCOPED_PKG_REGEXP = /(?:^|\/)(@[^\/?]+?)(?=%2f)/;
+// `(?=%2f|\/)` Match SCOPE_SEPARATOR, the escaped '/', or a raw `/` and don't capture
+// The reason for matching a plain `/` is NPM registry being inconsistent about escaping `/` in
+// scoped package names: when you're fetching a tarball, it is not escaped, when you want info
+// about the package, it is escaped.
+const SCOPED_PKG_REGEXP = /(?:^|\/)(@[^\/?]+?)(?=%2f|\/)/;
 
 // TODO: Use the method from src/cli/commands/global.js for this instead
 function getGlobalPrefix(): string {