Add a semantic token type for char literals

The LSP spec doesn't recognise character literals, so
had to extend the suported types to our own custom type

crates/rust-analyzer/src/semantic_tokens.rs

@@ -44,6 +44,7 @@ define_semantic_token_types![
     (BRACE, "brace"),
     (BRACKET, "bracket"),
     (BUILTIN_TYPE, "builtinType"),
+    (CHAR_LITERAL, "characterLiteral"),
     (COMMA, "comma"),
     (COLON, "colon"),
     (DOT, "dot"),