fix: make signature info response conform to spec

This addreses
#10464.

This patch picks up `lsp-types` 0.90.1, which serialises the
`SignatureInformation` and `ParameterInformation` with the right casing.
It also adds `activeSignature` field as part of the top-level signature
response. It keeps `activeParameter` at the top-level for backwards
compatibility.

Author: Alex Muscar

Cargo.lock

@@ -22,7 +22,7 @@ crossbeam-channel = "0.5.0"
 dissimilar = "1.0.2"
 itertools = "0.10.0"
 jod-thread = "0.1.0"
-lsp-types = { version = "0.90.0", features = ["proposed"] }
+lsp-types = { version = "0.90.1", features = ["proposed"] }
 parking_lot = "0.11.0"
 xflags = "0.2.1"
 oorandom = "11.1.2"

crates/rust-analyzer/Cargo.toml

@@ -399,7 +399,7 @@ pub(crate) fn signature_help(
     };
     lsp_types::SignatureHelp {
         signatures: vec![signature],
-        active_signature: None,
+        active_signature: Some(0),
         active_parameter,
     }
 }