Fix TimeZoneInfo.Equals and TimeZoneInfo.HasSameRules

[RenderMichael]

Based on #88641 (comment)

On Linux, different UTC aliases for produce TimeZoneInfos which have all the same rules, but some have _adjustmentRules == null and others _adjustmentRules == []. The corresponding API GetAdjustmentRules() returns an empty array if the underlying value is null:

runtime/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

Lines 140 to 146 in a3c21b9

	public AdjustmentRule[] GetAdjustmentRules()
	{
	if (_adjustmentRules == null)
	{
	return Array.Empty<AdjustmentRule>();
	}

runtime/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs

Lines 81 to 87 in a3c21b9

	public AdjustmentRule[] GetAdjustmentRules()
	{
	if (_adjustmentRules == null)
	{
	return Array.Empty<AdjustmentRule>();
	}

Which implies that these two values are equivalent.

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Issue Details

---

Based on #88641 (comment)

On Linux, different UTC aliases for produce TimeZoneInfos which have all the same rules, but some have _adjustmentRules == null and others _adjustmentRules == []. The corresponding API GetAdjustmentRules() returns an empty array if the underlying value is null:

runtime/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

Lines 140 to 146 in a3c21b9

	public AdjustmentRule[] GetAdjustmentRules()
	{
	if (_adjustmentRules == null)
	{
	return Array.Empty<AdjustmentRule>();
	}

runtime/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs

Lines 81 to 87 in a3c21b9

	public AdjustmentRule[] GetAdjustmentRules()
	{
	if (_adjustmentRules == null)
	{
	return Array.Empty<AdjustmentRule>();
	}

Which implies that these two values are equivalent.

Author:	RenderMichael
Assignees:	-
Labels:	community-contribution, area-System.DateTime
Milestone:	-

[RenderMichael]

Build failure is #88868, PTAL @tarekgh

[tarekgh]

@RenderMichael all failures are known unrelated issues https://github.com/dotnet/runtime/pull/88869/checks?check_run_id=15059873081. Please try to look at the suggestion #88869 (comment).

[RenderMichael]

@tarekgh Glad there's a way to express the test's prerequisites in a less ad-hoc way! Ready for review