Merge definitions from all plugins for Document(Type)Definition message (#3846)

* Merge definitions from all plugins for Document(Type)Definition message

- enables multiple plugins to provide Document(Type)Definition for the same message

* Remove unnecessary head usage in ghcide TestUtils

* Use Nothing for original selection when upgrading Location to LocationLink

in combineResponses of plugins to TextDocumentDefinition message

* Share combineResponses document definition and document type definition tests

* Downgrade locations to links when missing client capability in combineResponses (plugin API)

- Upgrade locations to links only when necessary (some responses are links)

* Test preserving link data in combineResponses of Definition message

* Add haddock to mergeDefinitions in plugin API

* Replace usage of OverloadedRecordDot with lenses

- to support GHC < 9.2

* Add TypeFamilies extension to TypesTests to support GHC < 9.4

* Require focus >= 1.0.3.2 to fix 9.8 build for ghcide and hls-graph

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Co-authored-by: Michael Peyton Jones <me@michaelpj.com>

Author: JiriLojda