Swift: better join order fix for NamedPattern.getVarDecl

This brings it down to 85ms when run from a query, not just from quick-eval:

```

[2023-06-14 14:47:06] Evaluated non-recursive predicate NamedPattern#1696c0d8::NamedPattern::getVarDecl#0#dispred#ff@04392e6o in 85ms (size: 91309).
Evaluated relational algebra for predicate NamedPattern#1696c0d8::NamedPattern::getVarDecl#0#dispred#ff@04392e6o with tuple counts:
        1310544   ~9%    {2} r1 = SCAN var_decls OUTPUT In.0, In.1
        1209062   ~0%    {2} r2 = STREAM DEDUP r1
        1209062   ~0%    {2} r3 = JOIN r2 WITH Synth#5f134a93::Synth::convertVarDeclToRaw#1#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
          91309   ~0%    {3} r4 = JOIN r3 WITH VarDecl#914e0d1e::Generated::VarDecl::getImmediateParentPattern#0#dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0

          69599   ~0%    {3} r5 = JOIN r4 WITH #Pattern#19b8cf65::Pattern::getImmediateEnclosingPattern#0#dispredPlus#bf_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2

         160908   ~1%    {3} r6 = r4 UNION r5
          94246   ~0%    {4} r7 = JOIN r6 WITH Synth#5f134a93::Synth::convertNamedPatternToRaw#1#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.0
          91309   ~1%    {2} r8 = JOIN r7 WITH named_patterns ON FIRST 2 OUTPUT Lhs.3, Lhs.2
                         return r8
```

Author: d10c

swift/ql/lib/codeql/swift/elements/pattern/NamedPattern.qll

@@ -20,8 +20,7 @@ class NamedPattern extends Generated::NamedPattern {
    */
   VarDecl getVarDecl() {
     this.getImmediateEnclosingPattern*() = result.getImmediateParentPattern() and
-    pragma[only_bind_out](pragma[only_bind_into](result).getName()) =
-      pragma[only_bind_out](pragma[only_bind_into](this).getName())
+    pragma[only_bind_out](result.getName()) = pragma[only_bind_out](this.getName())
   }
 
   override string toString() { result = this.getName() }