Rendered Markdown diff in Source Control turns tables into raw pipes and dashes

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.134.0 (110a328ea54b42367b803ec53ee0bf52ef26b419, arm64)
- OS Version: macOS 26.5 (Darwin 25.5.0), arm64

Steps to Reproduce:

1. Commit a Markdown file that contains a table.
2. Edit one cell so that the column gets wider. A formatter that re-aligns the pipes then rewrites every row of the table.
3. Open the file from the Source Control view.
4. Run **Reopen Editor With…** and choose **Markdown Preview**.

## Actual

The modified side no longer shows a table. The whole table turns into a run of literal pipes and dashes, which is unreadable and makes the change impossible to review. The other side still shows the same table correctly.

On the left, the unmodified revision renders as a table. On the right, the modified revision, where a single cell was edited:

It is at its worst when a column changes width, because every row of the table then gets rewritten even though only one cell changed.

## Expected

Each side renders its own table, so the comparison is between two readable tables.

## Related

#332107 looks related: Mermaid code blocks are also broken in the rendered Source Control diff.