Remove #region directives from Android.Runtime.XmlReaderPullParser

[Copilot]

XmlReaderPullParser.cs still used #region/#endregion, which conflicts with repository style (no #region). This change removes those directives while preserving section intent as inline comments.

• Scope

  • Updated only src/Mono.Android/Android.Runtime/XmlReaderPullParser.cs.
  • No functional/API changes; this is a formatting/convention cleanup.

• Directive cleanup

  • Converted:
    • #region IXmlResourceParser implementation → // IXmlResourceParser implementation
    • #region IAttributeSet implementation → // IAttributeSet implementation
    • #region IXmlPullParser implementation → // IXmlPullParser implementation
  • Removed the three corresponding #endregion lines.

• Result

  • Section labeling remains readable.
  • File no longer contains #region/#endregion.

// IXmlPullParser implementation
public void DefineEntityReplacementText (string? entityName, string? replacementText)
{
	throw new NotSupportedException ();
}