Implement IUtf8SpanFormattable on DateTime, DateTimeOffset, DateOnly, TimeOnly, TimeSpan, Char, Rune

[stephentoub]

Contributes to #81500

(Note that we have a fair amount of code duplication between various formatters (like the DateTimeFormat helper updated in this PR), FormattingHelpers used by Utf8Formatter, and Number.Formatting.cs used by formatting for our primitives. I've done a little consolidation in this PR, but there's a lot more than can / should be done. We're also inconsistent as to whether we're working in terms of spans, refs, or pointers, which leads to more duplication. That can also be consolidated further subsequently.)

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Issue Details

---

Contributes to #81500

(Note that we have a fair amount of code duplication between various formatters (like the DateTimeFormat helper updated in this PR), FormattingHelpers used by Utf8Formatter, and Number.Formatting.cs used by formatting for our primitives. I've done a little consolidation in this PR, but there's a lot more than can / should be done. We're also inconsistent as to whether we're working in terms of spans, refs, or pointers, which leads to more duplication. That can also be consolidated further subsequently.)

Author:	stephentoub
Assignees:	-
Labels:	area-System.Runtime
Milestone:	8.0.0

[stephentoub]

private DateTime _dt = new DateTime(2023, 04, 06, 10, 37, 12, DateTimeKind.Utc);
private TimeSpan _ts = TimeSpan.FromSeconds(12345.6789);
private char[] _chars = new char[100];
private byte[] _bytes = new byte[100];

[Benchmark] public bool DT_Char_R() => _dt.TryFormat(_chars, out _, "r");
[Benchmark] public bool DT_Char_O() => _dt.TryFormat(_chars, out _, "o");
[Benchmark] public bool DT_Char_Rfc1123() => _dt.TryFormat(_chars, out _, DateTimeFormatInfo.InvariantInfo.RFC1123Pattern);
[Benchmark] public bool TS_Char_C() => _ts.TryFormat(_chars, out _, "c");
[Benchmark] public bool TS_Char_G() => _ts.TryFormat(_chars, out _, "G");

[Benchmark] public bool UTF8Formatter_DT_R() => Utf8Formatter.TryFormat(_dt, _bytes, out _, new StandardFormat('R'));
[Benchmark] public bool UTF8Formatter_DT_O() => Utf8Formatter.TryFormat(_dt, _bytes, out _, new StandardFormat('O'));
[Benchmark] public bool UTF8Formatter_TS_C() => Utf8Formatter.TryFormat(_ts, _bytes, out _, default);
[Benchmark] public bool UTF8Formatter_TS_G() => Utf8Formatter.TryFormat(_ts, _bytes, out _, new StandardFormat('G'));

Method	Toolchain	Mean	Error	StdDev	Ratio
DT_Char_R	\main\corerun.exe	21.79 ns	0.220 ns	0.206 ns	1.00
DT_Char_R	\pr\corerun.exe	19.25 ns	0.376 ns	0.352 ns	0.88
DT_Char_O	\main\corerun.exe	27.67 ns	0.171 ns	0.151 ns	1.00
DT_Char_O	\pr\corerun.exe	24.99 ns	0.162 ns	0.144 ns	0.90
DT_Char_Rfc1123	\main\corerun.exe	179.71 ns	1.347 ns	1.194 ns	1.00
DT_Char_Rfc1123	\pr\corerun.exe	175.81 ns	1.055 ns	0.881 ns	0.98
TS_Char_C	\main\corerun.exe	23.47 ns	0.176 ns	0.164 ns	1.00
TS_Char_C	\pr\corerun.exe	21.51 ns	0.127 ns	0.112 ns	0.92
TS_Char_G	\main\corerun.exe	33.72 ns	0.210 ns	0.186 ns	1.00
TS_Char_G	\pr\corerun.exe	32.16 ns	0.666 ns	0.712 ns	0.96
UTF8Formatter_DT_R	\main\corerun.exe	18.47 ns	0.101 ns	0.095 ns	1.00
UTF8Formatter_DT_R	\pr\corerun.exe	18.60 ns	0.075 ns	0.062 ns	1.01
UTF8Formatter_DT_O	\main\corerun.exe	23.76 ns	0.095 ns	0.084 ns	1.00
UTF8Formatter_DT_O	\pr\corerun.exe	25.30 ns	0.084 ns	0.078 ns	1.06
UTF8Formatter_TS_C	\main\corerun.exe	21.20 ns	0.130 ns	0.115 ns	1.00
UTF8Formatter_TS_C	\pr\corerun.exe	19.19 ns	0.062 ns	0.058 ns	0.90
UTF8Formatter_TS_G	\main\corerun.exe	22.57 ns	0.254 ns	0.212 ns	1.00
UTF8Formatter_TS_G	\pr\corerun.exe	22.44 ns	0.071 ns	0.060 ns	0.99

[EgorBo]

Improvements on arm64:

• [Perf] Windows/arm64: 21 Improvements on 4/17/2023 5:51:51 AM perf-autofiling-issues#16767
• [Perf] Windows/arm64: 4 Improvements on 4/17/2023 1:05:21 AM perf-autofiling-issues#16757
• [Perf] Windows/arm64: 4 Improvements on 4/17/2023 5:51:51 AM perf-autofiling-issues#16777

x64:

• [Perf] Alpine/x64: 6 Improvements on 4/9/2023 11:24:15 AM perf-autofiling-issues#17049