[Discover] Deangularize discover controller

[kertal]

Summary

This PR reduces Discover's Angular controller to a minimum (mainly router functions).

Changes

• Most of discover.js logic is migrated into hooks and a wrapper component, only URL logic is left behind (Future PR)
• Clicking on "Reset search" when loading a saved search no longer reloads the whole URL
• Switching index patterns no longer reloads the whole URL
• URL reload only happens when a saved search is saved, loaded or New is selected (will remove that once we migrate the while plugin to react router)
• Lots of files were moved for a better directory structure, so files just relevant to the main part of Discover can be found here: src/plugins/discover/public/application/apps/main/
• Due to the usage of Observables the number initial number of re-renderings of the layout when loading the component was reduced to 3 (originally it was 6+), when clicking on 'Reload', only 2 re-renderings take place

Note that splitting the single request into 3 requests for number of hits, aggregation data for the histogram and documents was part of this PR, but for a better scope this was removed and there will be the follow up PR #100326.

Reviewing

Best to start with the new controller like component DiscoverMainApp

https://github.com/elastic/kibana/blob/b78f2b13404b56873e0b428d883354a55970028c/src/plugins/discover/public/application/apps/main/discover_main_app.tsx

It contains the old controller logic splitted into 4 hooks , useDiscoverState, useUrl, useSearchSession,useSavedSearchData, and some inline code

The majority of other changes are just different paths, so I'd recommend using Github's viewed button, and then to review the relevant stuff

Testing

There shall be no regressions!

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[flash1293]

Tested around and didn't manage to break it, LGTM

This definitely needs at least one other pair of eyes due to the large complexity involved.

[kertal]

It looks like restoring a search session with a relative time range doesn't work.
The problem is that the time range inside the original search is different from the ones saved inside a search session object. So that when the session is restored time ranges don't match.

@Dosant thx for the hint, I've adapted the code and added a test for this

Also noticed that when you successfully restored a session and then navigate away from it by doing a state change (e.g time change), then you get two network requests. I didn't check master for this, so not sure if this is a regression, but it looks like an indication that there are further possible state mgmt optimizations that would reduce re-renderings. Might be something worth debugging:

also fixed this, could you have another look? many thx!

[Dosant]

#96766 (comment)

Retested those pieces. LGTM 👍

[timroes]

Despite my minor comments left, code LGTM. I'd see some optimizations especially around how we could optimize state handling in the saved search and state hook, but I am fine having those done in another PR, since we should get this PR through to unblock other work.

Tested it on Chrome Linux with playing around in Discover a bit and couldn't find anything breaking so far.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 996f1fc
• Storybooks Preview
• Documentation Changes

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
discover	369	377	+8

Async chunks

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

id	before	after	diff
discover	420.9KB	426.4KB	+5.5KB

Page load bundle

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

id	before	after	diff
data	839.6KB	839.7KB	+70.0B
discover	74.8KB	74.5KB	-279.0B
total			-209.0B

History

• 💔 Build #129487 failed c823cd0
• 💚 Build #129431 succeeded 6d1b9b7
• 💔 Build #129374 failed fc677b3
• 💚 Build #129146 succeeded be7d95f
• 💚 Build #129094 succeeded 4677322

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @kertal