Merge #3062

3062: Implement slice pattern AST > HIR lowering r=jplatte a=jplatte

WIP. The necessary changes for parsing are implemented, but actual inference is not yet. Just wanted to upload what I've got so far so it doesn't get duplicated :)

Will fix #3043

Co-authored-by: Jonas Platte <jplatte+git@posteo.de>

crates/ra_syntax/src/ast/generated.rs

@@ -2117,7 +2117,11 @@ impl AstNode for SlicePat {
         &self.syntax
     }
 }
-impl SlicePat {}
+impl SlicePat {
+    pub fn args(&self) -> AstChildren<Pat> {
+        AstChildren::new(&self.syntax)
+    }
+}
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct RangePat {
     pub(crate) syntax: SyntaxNode,