Rust: Fix bad joins

```
Evaluated relational algebra for predicate _Synth::Synth::TFormatArgument#5cbf2ffd_63#join_rhs__Format::Format.getArgumentRef/0#dispred#38d664c__#antijoin_rhs@889ee4br with tuple counts:
           11356  ~0%    {5} r1 = JOIN `_Format::Format.getArgumentRef/0#dispred#38d664cb_Format::Format.getParent/0#dispred#f6ec3e8b_10#joi__#shared` WITH Synth::Synth::TFormatArgument#5cbf2ffd_63#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.3, Lhs.0
        19631351  ~0%    {6}    | JOIN WITH name_texts_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.0
           45933  ~0%    {6}    | JOIN WITH format_args_arg_names_10#join_rhs ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.5
             747  ~0%    {5}    | JOIN WITH format_args_expr_args_02#join_rhs ON FIRST 2 OUTPUT Lhs.0, Lhs.2, Lhs.3, Lhs.4, Lhs.5
                         return r1

Evaluated relational algebra for predicate __Format::Format.getParent/0#dispred#f6ec3e8b_FormatArgument::FormatArgument.getParent/0#dispred#864__#antijoin_rhs@01d9d70k with tuple counts:
        19631351  ~1%    {6} r1 = JOIN `_Format::Format.getParent/0#dispred#f6ec3e8b_FormatArgument::FormatArgument.getParent/0#dispred#8641__#shared` WITH name_texts_10#join_rhs ON FIRST 1 OUTPUT Lhs.4, Lhs.0, Lhs.1, Lhs.2, Lhs.3, Rhs.1
         5173010  ~0%    {7}    | JOIN WITH format_args_expr_args ON FIRST 1 OUTPUT Rhs.2, Lhs.5, Lhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.0
             747  ~0%    {5}    | JOIN WITH format_args_arg_names ON FIRST 2 OUTPUT Lhs.2, Lhs.3, Lhs.4, Lhs.5, Lhs.6
                         return r1

Evaluated relational algebra for predicate _NamedFormatArgument::NamedFormatArgument#18940f8e__Format::Format.getParent/0#dispred#f6ec3e8b_10#j__#antijoin_rhs@dafbd6hr with tuple counts:
           11356  ~0%    {5} r1 = JOIN `_Format::Format.getParent/0#dispred#f6ec3e8b_10#join_rhs_FormatArgument::FormatArgument.getParent/0#__#shared` WITH NamedFormatArgument::NamedFormatArgument#18940f8e ON FIRST 1 OUTPUT Rhs.4, Lhs.1, Lhs.2, Lhs.3, Lhs.0
        19631351  ~0%    {6}    | JOIN WITH name_texts_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.0
           45933  ~0%    {6}    | JOIN WITH format_args_arg_names_10#join_rhs ON FIRST 1 OUTPUT Lhs.1, Rhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.5
             747  ~0%    {5}    | JOIN WITH format_args_expr_args_02#join_rhs ON FIRST 2 OUTPUT Lhs.0, Lhs.2, Lhs.3, Lhs.4, Lhs.5
                         return r1

```

Author: hvitved

rust/ql/lib/codeql/rust/elements/internal/FormatTemplateVariableAccessConstructor.qll

@@ -17,17 +17,13 @@ predicate constructFormatTemplateVariableAccess(Raw::FormatArgsExpr parent, int
   unboundNamedFormatArgument(parent, index, kind, _)
 }
 
-/**
- * A named format argument for which no binding is found in the parent `FormatArgsExpr::getArg(_)`.
- * INTERNAL: Do not use.
- */
-predicate unboundNamedFormatArgument(
-  Raw::FormatArgsExpr parent, int index, int kind, NamedFormatArgument arg
+pragma[nomagic]
+private predicate formatArgsHasArg(
+  Raw::FormatArgsExpr parent, NamedFormatArgument arg, string name, int index, int kind
 ) {
-  exists(Format format, string name |
-    not parent.getArg(_).getName().getText() = name and
+  exists(Format format |
+    parent = Synth::convertFormatArgsExprToRaw(format.getParent()) and
     name = arg.getName() and
-    Synth::convertFormatArgsExprToRaw(format.getParent()) = parent and
     format.getIndex() = index
   |
     arg = format.getArgumentRef() and kind = 0
@@ -37,3 +33,21 @@ predicate unboundNamedFormatArgument(
     arg = format.getPrecisionArgument() and kind = 2
   )
 }
+
+pragma[nomagic]
+private predicate formatArgsHasArgName(Raw::FormatArgsExpr parent, string name) {
+  parent.getArg(_).getName().getText() = name
+}
+
+/**
+ * A named format argument for which no binding is found in the parent `FormatArgsExpr::getArg(_)`.
+ * INTERNAL: Do not use.
+ */
+predicate unboundNamedFormatArgument(
+  Raw::FormatArgsExpr parent, int index, int kind, NamedFormatArgument arg
+) {
+  exists(string name |
+    formatArgsHasArg(parent, arg, name, index, kind) and
+    not formatArgsHasArgName(parent, name)
+  )
+}