Completion item detail, description, and tag

[matoous]

In latest version of LSP (3.17) there seems to be a few new completion features that are not supported by helix but could be useful. Specifically:

• tagSupport - for now supports only deprecated tag that could for example render the item with strike-through.
• CompletionItemLabelDetails
  • detail to show additional details about the completion item, such as function signature/type annotation
  • description for fully qualified names/file paths
• preselect (already available in older versions) - could let the LSP decide which item to preselect, in our case it's currently always the first item. see: LSP Completion preselect and preview doc #2705

For full documentation see: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#textDocument_completion

[archseer]

Preselect is here #2705