Add span-based Uri {Try}{Un}EscapeDataString overloads

[MihaZupan]

Closes #40603

namespace System
{
    partial class Uri
    {
        public static string EscapeDataString(ReadOnlySpan<char> charsToEscape);
        public static bool TryEscapeDataString(ReadOnlySpan<char> charsToEscape, Span<char> destination, out int charsWritten);

        public static string UnescapeDataString(ReadOnlySpan<char> charsToUnescape);
        public static bool TryUnescapeDataString(ReadOnlySpan<char> charsToUnescape, Span<char> destination, out int charsWritten);
    }
}

The test coverage for these was not great, so I added a bunch more combinations. I also moved similar test cases from System.Runtime.Tests into the Uri project.

I updated FormUrlEncodedContent to also use these, so it's now allocating a lot less. For a random usage I pulled from eShopOnWeb tests:

Method	Toolchain	Mean	Error	Ratio	Allocated	Alloc Ratio
EShopOnWebLogin	main	513.7 ns	1.69 ns	1.00	2080 B	1.00
EShopOnWebLogin	pr	291.3 ns	1.47 ns	0.57	592 B	0.28

Looking at something like YARP's EncodePath helper with ASP.NET Core's test paths, the difference is

Method	Scenario	Mean	Error	Ratio	Allocated	Alloc Ratio
Old	LongTestPath	95.51 ns	0.702 ns	1.00	400 B	1.00
New	LongTestPath	70.58 ns	0.291 ns	0.74	344 B	0.86
Old	LongT(...)rcent [24]	337.00 ns	2.713 ns	1.00	392 B	1.00
New	LongT(...)rcent [24]	198.49 ns	0.892 ns	0.59	280 B	0.71
Old	TestPath	67.28 ns	0.439 ns	1.00	112 B	1.00
New	TestPath	44.98 ns	0.129 ns	0.67	56 B	0.50

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Issue Details

---

Implements #40603

namespace System
{
    partial class Uri
    {
        public static string EscapeDataString(ReadOnlySpan<char> charsToEscape);
        public static bool TryEscapeDataString(ReadOnlySpan<char> charsToEscape, Span<char> destination, out int charsWritten);

        public static string UnescapeDataString(ReadOnlySpan<char> charsToUnescape);
        public static bool TryUnescapeDataString(ReadOnlySpan<char> charsToUnescape, Span<char> destination, out int charsWritten);
    }
}

The test coverage for these was not great, so I added a bunch more combinations. I also moved similar test cases from System.Runtime.Tests into the Uri project.

Author:	MihaZupan
Assignees:	-
Labels:	area-System.Net
Milestone:	9.0.0

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[stephentoub]

How do we know the input is ASCII?

[MihaZupan]

The input is a bunch of concatenated Uri.EscapeDataString results, which are always ASCII, and the encoding is Latin1.
I clarified it in the comment now.