Fix AnchorLayoutV2 deferred anchor initialization when replacing anchored controls during suspended layout

[LeafShi1]

Fixes #14500

Root Cause

Under AnchorLayoutV2, when an anchored control is replaced while its parent container is inside a SuspendLayout / ResumeLayout flow, anchor metadata initialization can be deferred.

During ResumeLayout -> PerformLayout, the parent temporarily sets LayoutSuspendCount to 1 as part of its internal layout execution. The existing AnchorLayoutV2 logic treated that state the same as an externally suspended layout state, so the newly added anchored control could still skip AnchorInfo initialization even though actual layout was already running.

Proposed changes

• Ensure AnchorLayoutV2 initializes missing AnchorInfo for anchored children immediately before anchored layout is applied, if that metadata is still missing.
• Update the internal AnchorLayoutV2 path so that real layout execution can bypass the deferred-layout guard when it is running inside the framework’s internal layout pass.
• Add a regression test that matches the customer repro pattern of replacing a Panel at runtime and verifies that the replacement panel continues to resize with the form, in AnchorLayoutTests.cs.

Customer Impact

• After this fix, apps using AnchorLayoutV2 that replace an anchored control at runtime inside a SuspendLayout / ResumeLayout block will have the replacement control resize correctly with the form. The manual Anchor toggle workaround is no longer needed.

Regression?

• No

Risk

• Minimal

Screenshots

Before

When using AnchorLayoutV2. resizing the window, one of the inner panels is resized incorrectly if replaced by an equivalent panel after the InitializeComponent().

BeforeChanges.mp4

After

Replaced anchored controls continue to resize correctly with the form.

AfterChanges.mp4

Test methodology

• Manually and unit test

Test environment(s)

• .net 11.0.0-preview.5.26227.104

Microsoft Reviewers: Open in CodeFlow