Fix WebClient url encoding regression

[MihaZupan]

Fixes #79731

#75896 introduced two subtle changes to how we encoded values in WebClient:

1. We are now encoding the ' character.
   • Previous behavior looks like a bug though - regression between Framework and Core, see TaskWebClientTest.UploadValues_Success test is failing #79731 (comment)
2. We started using upper-case letters for percent-encoding values instead of lower-case
   • It turns out WebUtility.UrlEncode and HttpUtility.UrlEncode differ only in this casing behavior ... because reasons

I updated the test to expect ' to be encoded to fix nr. 1, and swapped the implementation to use HttpUtility instead for nr. 2.

[ghost]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Fixes #79731

#75896 introduced two subtle changes to how we encoded values in WebClient:

1. We are now encoding the ' character.
   • Previous behavior looks like a bug though - regression between Framework and Core, see TaskWebClientTest.UploadValues_Success test is failing #79731 (comment)
2. We started using upper-case letters for percent-encoding values instead of lower-case
   • It turns out WebUtility.UrlEncode and HttpUtility.UrlEncode differ only in this casing behavior ... because reasons

I updated the test to expect ' to be encoded to fix nr. 1, and swapped the implementation to use HttpUtility instead for nr. 2.

Author:	MihaZupan
Assignees:	-
Labels:	area-System.Net.Http
Milestone:	8.0.0

[wfurt]

LGTM.
So we still have duplicate UrlEncode Implementations right? We may look at it as followup.

[MihaZupan]

Yeah there's duplication in HttpUtility and WebUtility implementations.
I never understood the point of having both of these.

[MihaZupan]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).