[HTTP] WinHTTP fix exception

[ManickaP]

As noted in the issue, the special-cased error code is used more widely than just for invalid Latin-1. So I'm removing the special casing and leaving the plain WinHttpException there.

Fixes #117391

[Copilot]

Pull Request Overview

This PR removes the special-case handling for invalid Latin-1 headers in WinHTTP and always surfaces a WinHttpException using the error code. It also cleans up the related resource string and updates tests to expect the new exception behavior.

• Remove FormatException branch for ERROR_INVALID_PARAMETER in header APIs
• Delete the net_http_invalid_header_value resource entry
• Update existing test to assert on WinHttpException details

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpHandler.cs	Replace special-cased FormatException with WinHttpException.CreateExceptionUsingLastError in AddRequestHeaders.
src/libraries/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpCookieContainerAdapter.cs	Mirror the exception change in ResetCookieRequestHeaders.
src/libraries/System.Net.Http.WinHttpHandler/src/Resources/Strings.resx	Remove the net_http_invalid_header_value entry.
src/libraries/Common/tests/System/Net/Http/HttpClientHandlerTest.cs	Update test to expect HttpRequestException with inner error code instead of FormatException.

Comments suppressed due to low confidence (1)

src/libraries/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpCookieContainerAdapter.cs:83

• The new behavior in ResetCookieRequestHeaders always throws a WinHttpException for invalid header values, but there’s no existing test for this scenario. Adding a unit test to cover invalid cookie header handling would ensure this change is validated.

                    throw WinHttpException.CreateExceptionUsingLastError(nameof(Interop.WinHttp.WinHttpAddRequestHeaders));

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[ManickaP]

/ba-g #117772