Improve Enqueued Assets report in Site Health

The current Site Health reports for the Enqueued Assets module, introduced in #25, do not include actionable information for users about how to address a site loading too many enqueued assets. As noted by @felixarntz here:

We also need to think about how to make this warning more actionable, e.g. at a minimum tell users which plugins or themes are responsible for enqueuing the majority of assets etc.

Suggestions for changes (in progress) are below.

Enqueued scripts

If acceptable

Current description: The amount of [#] enqueued scripts (size: [size]) is acceptable.

New description:

If not acceptable

Current description: Your website enqueues [#] scripts (size: [size]). Try to reduce the number or to concatenate them.

More info about performance optimization

Clean Test Cache

New description:

Enqueued styles

If acceptable

Current description: The amount of [#] enqueued styles (size: [size]) is acceptable.

New description:

If not acceptable

Current description: Your website enqueues [#] styles (size: [size]). Try to reduce the number or to concatenate them.

More info about performance optimization

Clean Test Cache

Start at the Enqueued Assets module's Site Health reports for enqueued scripts and styles, then review the existing descriptions and the context from issue #25. Done means the acceptable and unacceptable reports provide actionable guidance, including which plugins or themes contribute most assets, with updated tests for both scripts and styles.