Preload inline blame data

What does this MR do and why?

Preloads blame data when hovering on the Blame button to improve the perceived performance of this feature.

How Preloading Works

1. Hover on Blame button → triggers v-gl-hover-load directive
2. Event bubbles up → @preload-blame event reaches the blob viewer component
3. preloadBlame prop becomes true → triggers the watcher in the appropriate viewer
4. GraphQL query executes → fetches blame data in background
5. User clicks Blame → data is already available (or in flight), faster display

References

Screenshots or screen recordings

Before	After
Blame data takes a while to load after click	Blame data available faster after click

How to set up and validate locally

1. Enable the inline_blame feature flag
2. Open a file containing source code
3. Hover over the blame button and observe the network request make upon hover
4. Click the Blame button, the blame data should load faster than before

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.