Support generating SCIP/LSIF index

The Language Server Index Format and its (kind of) successor SCIP define language-independent formats for information dumps of a language server. It allows tools like code editors and online repositories (eg. supported by GitHub, GitLab) to provide some LSP features without requiring an entire language server instance running in the background.

The LSIF specification has currently not reached 1.0.0 status yet.
In its most recent specification, LSIF would allow for the following language features in offline situations:

• textDocument/definition
• textDocument/declaration
• textDocument/hover
• textDocument/references
• textDocument/implementation
• textDocument/typeDefinition
• textDocument/foldingRange
• textDocument/documentLink
• textDocument/documentSymbol
• textDocument/semanticTokens/full

I'm not entirely sure whether this topic has been discussed in this community before, I wasn't able to find any mentions here in the older issues. In my opinion it could be a great feature to have a way of extracting project information out of the LuaLS into LSIF files.

Non è indicato alcun file sorgente, test o punto di ingresso. Inizia confrontando le specifiche LSIF e SCIP con le informazioni che LuaLS espone già, quindi determina l'ambito della generazione degli indici di progetto. Il lavoro è completo quando LuaLS può estrarre le informazioni del progetto in un formato di indice supportato e il comportamento è coperto da test.