Fix WhiteSpace validation in HttpHeaders

[MihaZupan]

Fixes #102584

#86007 added a bit too much validation for header values. In a couple of places it was redundant with the checks we would do anyway (e.g. right before calling HeaderDescriptor.TryGet or HeaderUtilities.CheckValidToken), and in a few others it was more strict than the parsing validation that only looks for the ASCII space and horizontal tab.

In a couple of places we were also calling into validating constructors right after parsing, thus wasting cycles on validating twice.

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[MihaZupan]

@MihuBot fuzz HttpHeaders

[MihaZupan]

@EgorBot

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkRunner.Run<HeaderBenchmarks>(args: args);
//BenchmarkRunner.Run<HeaderBenchmarks>();

public class HeaderBenchmarks
{
    private readonly HttpRequestHeaders _request = new HttpRequestMessage().Headers;
    private readonly HttpResponseHeaders _response = new HttpResponseMessage().Headers;

    [Benchmark]
    public void Warning()
    {
        _request.Add("Warning", "001 Hello \"World\"");
        _request.Clear();
    }

    [Benchmark]
    public void ETag()
    {
        _response.Add("ETag", "\"foo\"");
        _response.Clear();
    }
}

[EgorBot]

Benchmark results on Intel

BenchmarkDotNet v0.13.12, Ubuntu 22.04.4 LTS (Jammy Jellyfish)
Intel Xeon Platinum 8370C CPU 2.80GHz, 1 CPU, 16 logical and 8 physical cores
  Job-ZQKWLS : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
  Job-VPTTUM : .NET 9.0.0 (42.42.42.42424), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	Toolchain	Mean	Error	Ratio
Warning	Main	130.19 ns	0.402 ns	1.00
Warning	PR	103.31 ns	0.428 ns	0.79
ETag	Main	67.21 ns	0.273 ns	1.00
ETag	PR	55.91 ns	0.469 ns	0.83

BDN_Artifacts.zip

[EgorBot]

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Usage example: link

[MihaZupan]

@dotnet/ncl any volunteers for reviewing this one?

[liveans]

@dotnet/ncl any volunteers for reviewing this one?

I will, but would be better to have one more eye on this

[liveans]

LGTM, just a question