DH-15686: Loading Spinner Stutter

[bmingles]

Description

The loading spinner stutters a bit when loading the page. It's only really noticeable when the page load takes long enough to see it such as when plugins are being loaded.

Supports DH-15686

Steps to reproduce

This can be seen locally when plugins are being loaded. A synthetic delay can be introduced in PluginUtils right after the manifest is loaded

await new Promise(resolve => {
  setTimeout(resolve, 5000);
});

Expected results

The spinner should rotate seamlessly

Actual results

It shifts a small bit and backtracks

Versions
0.26.0