feat: add missing [StringSyntax(DateTimeFormat)] to DateTimeOffset methods in BindConverter

[EduardF1]

Summary

This PR addresses issue #44535 by adding the missing [StringSyntax] attributes in BindConverter.cs.

Changes Made

A previous PR added [StringSyntax] annotations to the DateTime, DateOnly, and TimeOnly format overloads in BindConverter, but inadvertently omitted the equivalent DateTimeOffset overloads. This PR fixes that gap:

• FormatValue(DateTimeOffset value, string format, ...) → [StringSyntax(StringSyntaxAttribute.DateTimeFormat)]
• FormatValue(DateTimeOffset? value, string format, ...) → [StringSyntax(StringSyntaxAttribute.DateTimeFormat)]
• TryConvertToDateTimeOffset(obj, culture, string format, ...) → [StringSyntax(StringSyntaxAttribute.DateTimeFormat)]
• TryConvertToNullableDateTimeOffset(obj, culture, string format, ...) → [StringSyntax(StringSyntaxAttribute.DateTimeFormat)]

Investigation of Remaining Format Types

The issue also listed EnumFormat, GuidFormat, NumericFormat, and TimeSpanFormat as remaining items. After a thorough audit of the codebase:

• GuidFormat: No public aspnetcore methods accept a Guid-specific format string (route constraints use Guid.TryParse without a format parameter).
• NumericFormat: BindConverter numeric FormatValue methods do not accept format strings. IHtmlGenerator.FormatValue(object, string) accepts object (not a typed numeric value), so annotating it with NumericFormat would be misleading/incorrect — as confirmed by closed draft PR #62179 which attempted exactly this and was not merged.
• TimeSpanFormat: No public aspnetcore methods take a TimeSpan-specific format string.
• EnumFormat: Enum formatting is handled internally by private methods that call �alue.ToString() with no user-supplied format string.

The BCL polyfill at src/Shared/CodeAnalysis/StringSyntaxAttribute.cs already defines all four constants — they're simply not applicable to any current public API surface in aspnetcore.

Fixes #44535

[dotnet-policy-service]

Thanks for your PR, @EduardF1. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Youssef1313]

Related past PR: #44663

@JamesNK @MackinnonBuck for review.

[EduardF1]

For visibility on the failing checks: I pulled the AzDO build timeline for build 1404094 and the two real failures are:

1. Run build.sh (Ubuntu x64) — error : Failed to convert '.../Microsoft.Extensions.Features.dll' to webcil: Could not find file '...Microsoft.Extensions.Features.dll' from Microsoft.NET.Sdk.WebAssembly.Browser.targets(364,5). Missing-artifact / build orchestration error, not produced by the source change.
2. Helix x64 Subset 1 — InMemory.FunctionalTests--net11.0 and Microsoft.AspNetCore.Server.Kestrel.Tests--net11.0 work items failed under Microsoft.DotNet.Helix.Sdk.MultiQueue.targets(91,5). Both are Kestrel/Hosting tests, completely independent of the BindConverter.cs change in this PR (which is purely metadata — adding [StringSyntax(StringSyntaxAttribute.DateTimeFormat)] to four already-existing parameters).

Build Analysis is just rolling those two up. Could a maintainer trigger a rerun — or, if these are known-flaky on main right now, ignore the gates? Happy to rebase if that helps.

[Youssef1313]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 4 pipeline(s).