[Reporting] Remove preserve_layout injected css

[jloleysens]

Summary

Closes #120348

This PR removes the global injection of app-specific styles in Screenshotting in preserve_layout except for two rules:

.hide-for-sharing {}

#globalBannerList {}

Both of which may introduce changes that are beyond the scope of this PR:

• .hide-for-sharing is used in a number of places, but can easily be removed and driven by JS (screenshotMode)
• #globalBannerList is perhaps slightly trickier since that code does not live inside of plugins (lives in core). We may have to leave this for now, although it is only present in preserve_layout screenshots. Perhaps it could safely be removed?

The primary motivation behind this is to move related code closer together, and out of Reporting which should not know anything about these apps. Functionally, this PR should not change anything. We should still have the same styles as before when taking screenshots (please test!). Per @tsullivan - we do have functional tests that should give more peace-of-mind for this refactor.

Additional notes

• In the future, we would like to experiment with introducing print media views for apps, this work will make it easier to work with apps in an isolated way.

[elasticmachine]

Pinging @elastic/kibana-reporting-services (Team:Reporting Services)

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesSv)

[jloleysens]

We can open up a follow-up issue to address this.

[tsullivan]

I think what you wrote about just doing this in JS within the screenshotting plugin is a good idea

[jloleysens]

@elasticmachine merge upstream

[kibana-ci]

💚 Build Succeeded

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• Commit: a07ac1f
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Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
visualizations	209	214	+5

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
visualizations	157.8KB	163.9KB	+6.0KB

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
visualizations	43.9KB	44.1KB	+143.0B

Unknown metric groups

async chunk count

id	before	after	diff
visualizations	10	11	+1

History

• 💔 Build #26566 failed de49f4b

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@elasticmachine merge upstream

[flash1293]

Tested and everything still seems to work fine

[tsullivan]

We should still have the same styles as before when taking screenshots (please test!).

There are a few automated tests that ensure that the latest PNG reports visually match a baseline image, which should give a lot of confidence here :)

[tsullivan]

LGTM