Reduce allocation in HttpUtility.UrlPathEncode.

[TrayanZapryanov]

Incorporate previously closed PR + feedback.
New benchmarks with slightly modified URL to contain non ascii characters.

[MemoryDiagnoser]
public class HttpUtilityBenchmarks
{
	[Benchmark]
	public bool UrlTryCreate() => Uri.TryCreate("http://EXAMPLE.NET/d\u00E9fault.xxx?sdsd=sds", UriKind.Absolute, out var uri);

	[Benchmark(Baseline = true)]
	public string UrlTryCreateAndUseAuthority() => Uri.TryCreate("http://EXAMPLE.NET/d\u00E9fault.xxx?sdsd=sds", UriKind.Absolute, out var uri) ? uri.Authority : "error";

	[Benchmark]
	public string UrlPathEncode() => HttpUtility.UrlPathEncode("http://EXAMPLE.NET/d\u00E9fault.xxx?sdsd=sds");

	[Benchmark]
	public string UrlPathEncode_PR() => MyHttpUtility.UrlPathEncode("http://EXAMPLE.NET/d\u00E9fault.xxx?sdsd=sds");
}

Results:

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
UrlTryCreate	305.1 ns	6.07 ns	7.68 ns	0.82	0.03	0.0677	568 B	0.86
UrlTryCreateAndUseAuthority	376.1 ns	4.76 ns	4.45 ns	1.00	0.00	0.0792	664 B	1.00
UrlPathEncode	437.4 ns	2.93 ns	2.45 ns	1.16	0.02	0.1211	1016 B	1.53
UrlPathEncode_PR	438.8 ns	6.04 ns	5.65 ns	1.17	0.02	0.0982	824 B	1.24

There is a small regression in worst scenario - I guess due to renting 2 arrays, but this saves quite a lot of allocations.
These are results for URL without non ascii chars: http://example.net:8080/default.xxx?sdsd=sds

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
UrlTryCreate	88.95 ns	0.692 ns	0.614 ns	0.35	0.00	0.0067	56 B	0.23
UrlTryCreateAndUseAuthority	257.24 ns	2.847 ns	2.663 ns	1.00	0.00	0.0286	240 B	1.00
UrlPathEncode	342.34 ns	4.357 ns	3.862 ns	1.33	0.02	0.0830	696 B	2.90
UrlPathEncode_PR	289.49 ns	3.168 ns	2.963 ns	1.13	0.02	0.0591	496 B	2.07

[MihaZupan]

Btw this one also hit a conflict after #102917 got merged

[TrayanZapryanov]

@MihaZupan Rebase done.

[MihaZupan]

Thanks