Swift: fix bad join order in NamedPattern.getVarDecl()

Ideally the EDB itself should contain a direct
reference from NamedPattern to VarDecl, not just a name,
but oh well, this join order works fine.

BEFORE:

```
[2023-06-08 11:40:01] Evaluated non-recursive predicate quick_eval#ff@60fe07kr in 6533ms (size: 91309).
Evaluated relational algebra for predicate quick_eval#ff@60fe07kr with tuple counts:
          1209062   ~3%    {2} r1 = SCAN VarDecl#914e0d1e::Generated::VarDecl::getName#0#dispred#ff OUTPUT In.1, In.0
        234687793   ~0%    {2} r2 = JOIN r1 WITH NamedPattern#c3d26570::Generated::NamedPattern::getName#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Lhs.1, Rhs.1
         19112791   ~0%    {3} r3 = JOIN r2 WITH VarDecl#914e0d1e::Generated::VarDecl::getImmediateParentPattern#0#dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.0, Lhs.1

         19112791   ~0%    {3} r4 = JOIN r3 WITH Element#e67432df::Generated::Element::resolve#bf ON FIRST 1 OUTPUT Rhs.1, Lhs.2, Lhs.1
            24647   ~0%    {2} r5 = JOIN r4 WITH Element#d22cfd66::Element::getFullyUnresolved#bf ON FIRST 2 OUTPUT Lhs.1, Lhs.2

         19112791   ~0%    {3} r6 = JOIN r3 WITH Element#e67432df::Generated::Element::resolve#bf ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
         19112791   ~3%    {3} r7 = JOIN r6 WITH Element#d22cfd66::Element::getFullyUnresolved#bf ON FIRST 1 OUTPUT Lhs.2, Rhs.1, Lhs.1
            66662   ~4%    {2} r8 = JOIN r7 WITH #Pattern#19b8cf65::Pattern::getImmediateEnclosingPattern#0#dispredPlus#bf ON FIRST 2 OUTPUT Lhs.0, Lhs.2

            91309   ~2%    {2} r9 = r5 UNION r8
                           return r9
```

AFTER:

```
[2023-06-08 11:55:26] Evaluated non-recursive predicate quick_eval#ff@fe906afo in 26ms (size: 91309).
Evaluated relational algebra for predicate quick_eval#ff@fe906afo with tuple counts:
         92048   ~0%    {3} r1 = SCAN NamedPattern#c3d26570::Generated::NamedPattern::getName#0#dispred#ff OUTPUT In.0, In.1, In.0

         82893   ~0%    {2} r2 = SCAN #Pattern#19b8cf65::Pattern::getImmediateEnclosingPattern#0#dispredPlus#fb#flipped OUTPUT In.1, In.0
         66417   ~1%    {3} r3 = JOIN r2 WITH NamedPattern#c3d26570::Generated::NamedPattern::getName#0#dispred#ff ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.0

        158465   ~0%    {3} r4 = r1 UNION r3
         94246   ~3%    {3} r5 = JOIN r4 WITH VarDecl#914e0d1e::Generated::VarDecl::getImmediateParentPattern#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
         91309   ~2%    {2} r6 = JOIN r5 WITH VarDecl#914e0d1e::Generated::VarDecl::getName#0#dispred#ff ON FIRST 2 OUTPUT Lhs.2, Lhs.0
                        return r6
```

Author: d10c

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

@@ -19,8 +19,9 @@ class NamedPattern extends Generated::NamedPattern {
    * This will be the case as long as the variable is subsequently used.
    */
   VarDecl getVarDecl() {
-    this.getImmediateEnclosingPattern*() = result.getParentPattern().getFullyUnresolved() and
-    result.getName() = this.getName()
+    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())
   }
 
   override string toString() { result = this.getName() }