fix(checkout): On the cart page, fix bundled item stock section showing title with no content

[bc-shawnwang]

What?

I just merged a PR: #2663 but found a display bug:
The bundled item section heading (e.g. "bundle1:") was rendered even when no stock data would be displayed, leaving a floating label with no content beneath it

So this PR is to fix that bug.

Details:

For each bundled item, uses assignVar/getVar to pre-compute three boolean display flags:

• showOnHandQty — show_quantity_on_hand + quantity_on_hand + quantity_backordered all truthy
• showBackorderedQty — show_quantity_on_backorder + quantity_backordered both truthy
• showBackorderMessage — show_backorder_message + backorder_message both truthy
• the entire stock section (including the item name label) is guarded by {{#or (getVar ...) ...}} so the title only renders when at least one condition is met (at least one field is displayed)

Requirements

• CHANGELOG.md entry added (required for code changes only)

Tickets / Documentation

Add links to any relevant tickets and documentation.

• PR to introduce backorder prompts on bundled items
• ...

Screenshots (if appropriate)

If no backorder prompts to show for bundled item

before fix:

🔴 picklist item title is displayed when no backorder prompts displayed

after fix:

✅ picklist item tile is NOT displayed when no backorder prompts displayed

if sth to show for the bundled item

before and after fix its the same: