Improve IPAddress to/from bytes perf

[stephentoub]

Also cleaned up some unnecessary !s with MemberNotNullWhen.

private IPAddress _addr1 = IPAddress.Parse("1.2.3.4").MapToIPv6();
private IPAddress _addr2 = IPAddress.Parse("2600:141b:13:781::356e");
private IPAddress _addr3 = IPAddress.Parse("2600:141b:13:781::356e");
private byte[] _ipv6Bytes = IPAddress.Parse("2600:141b:13:781::356e").GetAddressBytes();

[Benchmark] public bool IsIPv4MappedToIPv6_True() => _addr1.IsIPv4MappedToIPv6;
[Benchmark] public bool IsIPv4MappedToIPv6_False() => _addr2.IsIPv4MappedToIPv6;
[Benchmark] public IPAddress NewIPv6() => new IPAddress(_ipv6Bytes, 0);
[Benchmark] public bool WriteBytes() => _addr3.TryWriteBytes(_ipv6Bytes, out _);

Method	Toolchain	Mean	Ratio
IsIPv4MappedToIPv6_True	\main\corerun.exe	2.965 ns	1.00
IsIPv4MappedToIPv6_True	\pr\corerun.exe	1.094 ns	0.36
IsIPv4MappedToIPv6_False	\main\corerun.exe	1.210 ns	1.00
IsIPv4MappedToIPv6_False	\pr\corerun.exe	1.183 ns	0.98
NewIPv6	\main\corerun.exe	21.082 ns	1.00
NewIPv6	\pr\corerun.exe	14.129 ns	0.67
WriteBytes	\main\corerun.exe	12.068 ns	1.00
WriteBytes	\pr\corerun.exe	2.227 ns	0.18

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Issue Details

---

Also cleaned up some unnecessary !s with MemberNotNullWhen.

private IPAddress _addr1 = IPAddress.Parse("1.2.3.4").MapToIPv6();
private IPAddress _addr2 = IPAddress.Parse("2600:141b:13:781::356e");
private IPAddress _addr3 = IPAddress.Parse("2600:141b:13:781::356e");
private byte[] _ipv6Bytes = IPAddress.Parse("2600:141b:13:781::356e").GetAddressBytes();

[Benchmark] public bool IsIPv4MappedToIPv6_True() => _addr1.IsIPv4MappedToIPv6;
[Benchmark] public bool IsIPv4MappedToIPv6_False() => _addr2.IsIPv4MappedToIPv6;
[Benchmark] public IPAddress NewIPv6() => new IPAddress(_ipv6Bytes, 0);
[Benchmark] public bool WriteBytes() => _addr3.TryWriteBytes(_ipv6Bytes, out _);

Method	Toolchain	Mean	Ratio
IsIPv4MappedToIPv6_True	\main\corerun.exe	2.965 ns	1.00
IsIPv4MappedToIPv6_True	\pr\corerun.exe	1.094 ns	0.36
IsIPv4MappedToIPv6_False	\main\corerun.exe	1.210 ns	1.00
IsIPv4MappedToIPv6_False	\pr\corerun.exe	1.183 ns	0.98
NewIPv6	\main\corerun.exe	21.082 ns	1.00
NewIPv6	\pr\corerun.exe	14.129 ns	0.67
WriteBytes	\main\corerun.exe	12.068 ns	1.00
WriteBytes	\pr\corerun.exe	2.227 ns	0.18

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Net
Milestone:	-

[stephentoub]

/azp run runtime-extra-platforms

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Azure Pipelines successfully started running 1 pipeline(s).

[dakersnar]

Improvements https://github.com/dotnet/perf-autofiling-issues/issues/8818#issuecomment-1266628997 (and other improvements throughout the issue. We are filing all improvements and regressions from a single commit range in a single issue now, hence why this is so long and contains unrelated regressions)