[Performance] CSS Loading improvements

[adearriba]

PR Summary:

Why are these changes introduced?

1. Dawn loads many CSS files that it doesn't use depending on certain configuration.
2. Footer CSS is blocking and normally the footer is not immediately seen so it can be deferred to onload.

Edit: Additional perf improvements not related to CSS:

1. Reduce event listeners for "summary" and "location-form" elements.

What approach did you take?

Conditional CSS loading. Only load the CSS files when needed based on liquid variables that enable or disable certain functionality.

Other considerations

Decision log

#	Decision	Alternatives	Rationale	Downsides
1	Load CSS when needed	Current state: Load everything, every time	Only load when needed	To improve performance, the CSS should be created by component and sometimes separated by feature. This will enable to load only the required CSS instead. Of course this must be done with balance based on CSS size.
2	Reduce event listeners	Current state: querySelectorAll and apply event listeners per element	Use event delegation to reduce memory footprint	None

Visual impact on existing themes

Since the decision to load CSS is based on the settings, it should affect anyone.

Testing steps/scenarios

• Enable/Disable product ratings and check product-ratings component
• Test facets swatches and show-more components
• Test Announcement bar with more than 1 block
• Test Product quick add and volume pricing

Checklist

• Added PR summary for release notes
• Followed theme code principles
• Linted with Theme Check
• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility

[adearriba]

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