Indicate missing lines when loading big files

Description

From this comment:

suggestion: Looks like the performance fix was to show only the first 70 lines + the last one while the rest of the data loads in the background. For large files like the one mentioned in this issue, this can look a bit weird (especially on a slow connection!) 🤔

Maybe we want to show a loader somewhere, that things are still loading 🤷

Proposal

When a user visits a large file lets somehow indicate that the rest of the lines are still loading.