fix(replays): Guard against undefined frame.data in BreadcrumbWebVital

[sentry]

This PR fixes a TypeError: Cannot read properties of undefined (reading 'value') occurring in the BreadcrumbWebVital component.

Root Cause:
The BreadcrumbWebVital component attempts to access frame.data.value without ensuring frame.data is defined. While isWebVitalFrame checks the frame's op property, it does not guarantee the presence of the data field. Older replay SDK versions (specifically < 8.22.0) can produce web-vital span frames where the data field is entirely absent, leading to a runtime error when these frames are processed.

Fix:
Added a null guard (if (!frame.data) return null;) in static/app/components/replays/breadcrumbs/breadcrumbWebVital.tsx immediately after the isWebVitalFrame check. This ensures that the component gracefully handles frames with missing data by not rendering, preventing the TypeError.

Test:
Added a new test file static/app/components/replays/breadcrumbs/breadcrumbWebVital.spec.tsx with two test cases:

1. Verifies that the component renders nothing when frame.data is undefined (simulating the problematic legacy frames).
2. Verifies that the component renders correctly when frame.data is present.

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Fixes JAVASCRIPT-3B62

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