Fix $extension usage in older rancher systems

[aalves08]

Setup

• Rancher version: 2.12.7
• Rancher UI Extensions: Kubewarden 4.1.0
• Browser type & version: n/a

Describe the bug

Root cause for rancher/kubewarden-ui#1444 is that SortableTable uses $extension:

const pluginFormatter = this.$extension?.getDynamic('formatters', c.formatter);

but there's no this.$extension in 2.12.7

To Reproduce

Follow repro steps in rancher/kubewarden-ui#1444

Result
Some table cols are not displayed (ones using a formatter)

Expected Result

All table cols should display fine

Screenshots

Additional context

[github-actions]

🤖 Issue grooming analysis

All four primary grooming criteria are clearly satisfied:

1. Clear Problem Statement ✅ — The title is precise, the description identifies the exact root cause ($extension is undefined in Rancher 2.12.x), and the affected area (SortableTable column formatters) is well-scoped.

2. Acceptance Criteria ✅ — The expected result ("All table cols should display fine") is concrete and testable, and defines what a fix looks like for a bug of this kind.

3. Technical Details ✅ — The specific problematic code path is quoted (this.$extension?.getDynamic('formatters', c.formatter)), the affected Rancher version (2.12.7) and extension (Kubewarden 4.1.0) are identified, and a root-cause hypothesis is provided.

4. Reproducibility ✅ — Reproduction steps are referenced via rancher/kubewarden-ui#1444, which is an acceptable cross-reference for a regression bug with an established repro path.

Dependencies / Additional Information ✅ — Related issues are linked both upstream (the Kubewarden UI issue) and to prior work (#12332).

This analysis was generated automatically based on the repository's grooming checklist.

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