When using UnityWebRequest.SendWebRequest with timeout property set to a particular value that is smaller than the time required for a server to respond, UnityWebRequest won't timeout before but will wait full time until the server responds

To reproduce:

1. Download attached "WebRequestTimeoutIOS.zip" project and open in Unity
2. Open "SampleScene" scene
3. Build for iOS
4. Deploy the Xcode project to the iOS device
5. When App is launched press "Request Slow" button
6. Check Xcode Console

Expected result: Debug Log will show that response arrived after approximately 1 second
Actual result: Debug Log will show that response arrived after approximately 10 seconds

Notes:
- This issue happens only on iOS
- This issue does not reproduce on Android (Mono and IL2CPP) and Standalone

Tested with:
- iPhone 7, iOS: 10.2 - Reproduced
- iPhone 8 Plus, iOS: 12.2 - Reproduced
- VLNQA00277, Asus ROG Phone (ASUS_Z01QD), Android 8.1.0, CPU: Snapdragon 845 SDM845, GPU: Adreno (TM) 630 - Not Reproduced

Reproduced on Unity 2019.1.0a3, 2019.1.14f1, 2019.2.1f2 and 2019.3.0a11
Not reproduced on Unity 2019.1.0a2
Regression on Unity 2019.1.0a3