Remove the legacy types from the platform public contract

[mshustov]

Having removed the legacy plugin discovery we've got rid of the last pieces of the Legacy plugin system. We can clean up our public API from the legacy types added to ensure BWC with the legacy plugin system.
See kibana.d.ts, src/core/server/index.ts, src/core/public/index.ts.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[TinaHeiligers]

@mshustov There's no direct export of any deprecated legacy types in src/core/server/index.ts or src/core/public/index.ts. Do we need to dig into each type grouping and remove legacy types from there?
e.g
We still have LegacyRequest in ensureRawRequest that wasn't handled in #109243.
Similarly, we're still using LegacyRequest in:

1. ensureRawRequest
2. AuthHeadersStorage
3. AuthStateStorage
4. BasePath

There are others that have been marked as deprecated and from digging through, I've come up with the following list to remove, keep and ones I'm not sure about:

Could you add a check to those that are in the right category please? Those that aren't right, we can discuss as a team. cc @elastic/kibana-core

To Remove:

From src/core/server/*:

• httpServiceSetup.auth (use HttpServiceStart.auth instead)
• IRenderOptions.vars apparently should have been removed with ui_render_mixin.

From in src/core/public/*:

• CoreSetup.injectedMetadata (should have been removed when Add config value support in frontend to New Platform #41990 was handled with Expose whitelisted config values to client-side plugin #50641) TL;DR: used to share config between server and client in plugins. Replaced with PluginInitializerContext
• CoreStart.injectedMetadata (should have been removed when Add config value support in frontend to New Platform #41990 was handled with Expose whitelisted config values to client-side plugin #50641) TL;DR: used to share config between server and client in plugins. Replaced with PluginInitializerContext

To keep:

• SavedObjectsImportFailure.title —> sharing saved objects functionality
• SavedObjectsImportSuccess.createNewCopy —> sharing saved objects functionality
• UiSettingsParams.metric? —> using the ‘old’ ui_metric usage counters that we haven’t yet removed

Unknown

Should these be removed or do we need to keep them?

• SavedObjectsMigrationLogger: warning (use warn instead)
• AppLeaveHandler from AppLeaveDefaultAction doesn’t indicate when we’re going to remove the type
• onAppLeave and appBasePath from AppMountParameters
• AsyncPlugin I think there might still be some plugins relying on this?
• req and res in IHttpFetchError

[mshustov]

There's no direct export of any deprecated legacy types in src/core/server/index.ts or src/core/public/index.ts.

Then we can close the issue. We are interested in removing unused legacy types from public API mostly.

Do we need to dig into each type grouping and remove legacy types from there?
Should these be removed or do we need to keep them?

We need to come up with a plan to remove deprecated API eventually but it's not the highest priority right now. You can create a new issue listing your findings from To Remove section to track the deprecated API and their usage across the codebase.

Similarly, we're still using LegacyRequest in:

We need to reference Hapi.Request in the codebase. Probably we should remove substitute LegacyRequest type with Hapi.Requst to remove this ambiguity.

[TinaHeiligers]

I've created follow up issues to address the specific tasks from #77997 (comment). Closing this issue as there aren't any legacy types exported from the public core API.