Swift: clean up VarDecl, NamedPattern and SwitchStmt interactions

* `variables` under `CaseStmt` are now AST children, which solves
  orphan `VarDecl`s in that case
* reordered `CaseStmt` AST children to be `labels > variables > body`
  (was `body > labels`)
* made `NamedPattern::getVarDecl` an extracted property instead of
  `getName`
* The above led to duplicate DB entities because of a quirk in the
  Swift compiler code. This is solved by tweaking the extraction of
  `variables` under `CaseStmt` to not use `getCaseBodyVariables`.

swift/schema.py

@@ -868,7 +868,7 @@ class IsPattern(Pattern):
     sub_pattern: optional[Pattern] | child
 
 class NamedPattern(Pattern):
-    name: string
+    var_decl: VarDecl
 
 class OptionalSomePattern(Pattern):
     sub_pattern: Pattern | child
@@ -884,6 +884,7 @@ class TypedPattern(Pattern):
     type_repr: optional["TypeRepr"] | child
 
 @group("stmt")
+@qltest.test_with("SwitchStmt")
 class CaseLabelItem(AstNode):
     pattern: Pattern | child
     guard: optional[Expr] | child
@@ -948,10 +949,11 @@ class BreakStmt(Stmt):
     target_name: optional[string]
     target: optional[Stmt]
 
+@qltest.test_with("SwitchStmt")
 class CaseStmt(Stmt):
-    body: Stmt | child
     labels: list[CaseLabelItem] | child
-    variables: list[VarDecl]
+    variables: list[VarDecl] | child
+    body: Stmt | child
 
 class ContinueStmt(Stmt):
     target_name: optional[string]