langium/lsp: made LSP service minimum document state settings configurable in startLanguageServer(...)

* added opportunity to distinguish required documents states and workspace states
* relaxed some doc state requirements to increase the LS' responsiveness from 'IndexedReferences' to 'Linked', as it is sufficient that the current document is (ideally) linked and all required documents are in state 'ComputedScopes':
   completion, declaration, definition, typeDefinition, hover, semanticToken
* switched requirements of some services to workspace state 'IndexedReferences':
   findReferences, getImplementation, documentHighlight, callHierarchy, rename

Author: sailingKieler