Add XML documentation to DatePickerDialog.UpdateDate(DateTime)

[Copilot]

The hand-written .NET-friendly overload DatePickerDialog.UpdateDate(DateTime) was missing XML doc comments despite being a public API. This adds <summary>, <remarks>, and <param> to document the method's behavior and its 1-based→0-based month conversion.

/// <summary>
/// Sets the current date shown by the dialog using a <see cref="System.DateTime" />.
/// </summary>
/// <remarks>
/// This is a .NET-friendly overload that forwards to
/// <see cref="UpdateDate(int, int, int)" />, converting the 1-based
/// <see cref="System.DateTime.Month" /> to Android's 0-based month value.
/// </remarks>
/// <param name="date">The date to display in the dialog.</param>
public void UpdateDate (DateTime date)
{
    UpdateDate (date.Year, date.Month - 1, date.Day);
}

Documentation-only change; no behavior modifications.

[Copilot]

Pull request overview

Adds missing XML documentation to the public, hand-written .NET-friendly overload Android.App.DatePickerDialog.UpdateDate(DateTime), clarifying its forwarding behavior and the 1-based (DateTime.Month) to 0-based (Android) month conversion. This improves API documentation completeness without changing runtime behavior.

Changes:

• Added <summary>, <remarks>, and <param> XML docs for DatePickerDialog.UpdateDate(DateTime).
• Documented the month conversion behavior when forwarding to UpdateDate(int, int, int).