index.ts: Better Gmail loading initialisation logic

Instead of using a timeout, which may get executed prematurely, check
for the visibility of Gmail's `loading` screen. When it disappears from
view, we know we can safely initialise all our plugin features.

This allows us to, for example, try to ensure our `<style>` element gets
appended last. Now the sidebar actually gets hidden with our CSS rule
from 496ac03b0d6afb28db09998eb9944db2102ad49e since it can take
precedence over Gmail's asynchronously-loaded styles.

0 files changed, 0 insertions, 0 deletions