Fix LT-22265: If there are new 'common' columns show them by default

[jasonleenaylor]

This change is 

[Copilot]

Pull Request Overview

Fixes a user interface issue where new 'common' columns in XML browse views were not being displayed by default. The changes ensure that when loading column configurations, any new common columns that weren't previously saved are automatically added to the visible columns list.

• Tracks which possible columns are new (not in saved configuration)
• Automatically shows new columns marked as 'common' by default

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[Copilot]

Potential NullReferenceException if node.Attributes is null. The null-conditional operator protects against node.Attributes being null, but not against node.Attributes["label"] returning null when the "label" attribute doesn't exist.

Suggested change

	var possible = newPossibleColumns.Find(n => n.Attributes?["label"].Value == node.Attributes?["label"].Value);
	var possible = newPossibleColumns.Find(n =>
	n.Attributes != null &&
	n.Attributes["label"] != null &&
	node.Attributes != null &&
	node.Attributes["label"] != null &&
	n.Attributes["label"].Value == node.Attributes["label"].Value);

[Copilot]

Missing comma in comment. Should be 'If there is a corresponding possible column, remove it from the newPossibleColumns list.'

Suggested change

	// if there is a corresponding possible column remove it from the newPossibleColumns list.
	// if there is a corresponding possible column, remove it from the newPossibleColumns list.

[aror92]

@aror92 reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @jasonleenaylor)