Add a Document.language field (#37)

* Add a `Document.language` field

Previously, SCIP consumers had to infer the programming language based
on the `Document.relative_path` field. It's common for some programming
languages to support multiple file formats (example, `.ts` and `.tsx`
for TypeScript).

* Add more languages from the LSP spec

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/

* schema: Add more languages + rearrange.

* Mark docs/scip.md as generated.

* schema: Fix doc comment + regenerate.

* Use alphabetical order for langauges and rename for consistency with LSP

Co-authored-by: Varun Gandhi <[email protected]>

Author: olafurpg

.gitattributes

@@ -2,4 +2,5 @@ bindings/typescript/scip.ts linguist-generated=true
 bindings/go/scip/scip.pb.go linguist-generated=true
 bindings/rust/src/scip.rs linguist-generated=true
 bindings/haskell/src/Proto/**.hs linguist-generated=true
+docs/scip.md linguist-generated=true
 yarn.lock linguist-generated=true