Stepper: Move conservative lazy loading and optimize masterbar styles

[alshakero]

Related context: p1715786768590259-slack-C7YPUHBB2

Proposed Changes

• Stepper now loads every step the moment it loads. The intention was to lazy-load them to prevent showing the glowing WordPress logo during the flow. But apparently, the loading was not lazy enough and it was slowing other more important things down, like LCP. This makes Stepper only cache the next step¹.
• The masterbar loaded dashicons everywhere, even though they're only used when logged in. Loading these icons is very slow (500-800ms damage to the largest contentful paint).
• Don't wait for the geolocating request before rendering Stepper.

¹ Stepper is non-linear, so the next step is undefined, but most likely it is the next step in the flows set defined in the flow.

Why are these changes being made?

To improve UX.

Testing steps

1. Smoke test /setup/onboarding.
2. Smoke test /Home and make sure the masterbar looks good.

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-127220

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-127220&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-127220&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~14 bytes removed 📉 [gzipped])

name                   parsed_size           gzip_size
entry-stepper               -272 B  (-0.0%)      -14 B  (-0.0%)
entry-subscriptions         -249 B  (-0.0%)      -49 B  (-0.0%)
entry-main                  -249 B  (-0.0%)      -49 B  (-0.0%)
entry-login                 -249 B  (-0.0%)      -49 B  (-0.0%)
entry-domains-landing       -249 B  (-0.0%)      -49 B  (-0.0%)
entry-browsehappy           -249 B  (-0.1%)      -49 B  (-0.1%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~31038 bytes added 📈 [gzipped])

name               parsed_size         gzip_size
stepper-user-step     +97637 B  (new)   +31038 B  (new)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• blaze-dashboard
• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug stepper/more-conservaative-lazy-load on your sandbox.