Implement named argument completion

Author: AJenbo

src/completion/mod.rs

@@ -5,7 +5,9 @@
 /// - **resolver**: Resolving the subject to a concrete class type
 /// - **builder**: Building LSP `CompletionItem`s from resolved class info
 /// - **phpdoc**: PHPDoc tag completion inside `/** … */` blocks
+/// - **named_args**: Named argument completion inside function/method call parens
 pub mod builder;
+pub mod named_args;
 pub mod phpdoc;
 pub mod resolver;
 pub mod target;