Ruby: Fix bad join-order in BarrierGuard::getABarrierNode

Before
```
Evaluated relational algebra for predicate XSS#e59174e9::Shared::Sanitizer#class#f@6c9d334e with tuple counts:
                 0   ~0%    {1} r1 = JOIN ActionView#3462bac2::RailsHtmlEscaping#f WITH project#DataFlowPublic#e1781e31::CallNode::getArgument#1#dispred#fff#3 ON FIRST 1 OUTPUT Lhs.0

            554860   ~0%    {2} r2 = JOIN SsaImpl#ff97b16a::Cached::getARead#1#ff_10#join_rhs WITH DataFlowPrivate#462ff392::Cached::TExprNode#ff ON FIRST 1 OUTPUT Lhs.1, Rhs.1

                 1   ~0%    {1} r3 = JOIN r2 WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstArrayInclusionCall#::getAMaybeGuardedCapturedDef#0#f ON FIRST 1 OUTPUT Lhs.1

                 1   ~0%    {1} r4 = r1 UNION r3

                 7   ~0%    {1} r5 = JOIN r2 WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstCompare#::getAMaybeGuardedCapturedDef#0#f ON FIRST 1 OUTPUT Lhs.1

           3045081   ~1%    {3} r6 = JOIN DataFlowPrivate#462ff392::Cached::TExprNode#ff_10#join_rhs WITH DataFlowPrivate#462ff392::Cached::TExprNode#ff_10#join_rhs ON FIRST 1 OUTPUT Lhs.1, Lhs.0, Rhs.1
           3045081   ~1%    {3} r7 = JOIN r6 WITH ControlFlowGraph#46cebcbd::CfgNode::getBasicBlock#0#dispred#ff ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Rhs.1
            554860   ~1%    {3} r8 = JOIN r7 WITH SsaImpl#ff97b16a::Cached::getARead#1#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
        1462917146   ~0%    {3} r9 = JOIN r8 WITH SsaImpl#ff97b16a::Cached::getARead#1#ff ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Rhs.1
           5082692   ~1%    {4} r10 = JOIN r9 WITH DataFlowPublic#e1781e31::guardControlsBlock#3#fff_102#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.2, Rhs.2, Lhs.1

                33   ~0%    {1} r11 = JOIN r10 WITH BarrierGuards#2462899b::stringConstArrayInclusionCall#3#fff ON FIRST 3 OUTPUT Lhs.3

                57   ~0%    {1} r12 = JOIN r10 WITH BarrierGuards#2462899b::stringConstCompare#3#fff ON FIRST 3 OUTPUT Lhs.3

                90   ~0%    {1} r13 = r11 UNION r12
                97   ~0%    {1} r14 = r5 UNION r13
                98   ~0%    {1} r15 = r4 UNION r14
                            return r15
```

After
```
[2022-10-17 20:35:01] Evaluated non-recursive predicate XSS#e59174e9::Shared::Sanitizer#class#f@487a64ar in 65ms (size: 98).
Evaluated relational algebra for predicate XSS#e59174e9::Shared::Sanitizer#class#f@487a64ar with tuple counts:
             0   ~0%    {1} r1 = JOIN ActionView#3462bac2::RailsHtmlEscaping#f WITH project#DataFlowPublic#e1781e31::CallNode::getArgument#1#dispred#fff#3 ON FIRST 1 OUTPUT Lhs.0

            33   ~0%    {1} r2 = JOIN DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstArrayInclusionCall#::guardChecksSsaDef#3#fff WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstArrayInclusionCall#::guardControlsSsaDef#4#ffff ON FIRST 3 OUTPUT Rhs.3

            33   ~0%    {1} r3 = r1 UNION r2

            57   ~1%    {1} r4 = JOIN DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstCompare#::guardChecksSsaDef#3#fff WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstArrayInclusionCall#::guardControlsSsaDef#4#ffff ON FIRST 3 OUTPUT Rhs.3

        554860   ~0%    {2} r5 = JOIN SsaImpl#ff97b16a::Cached::getARead#1#ff_10#join_rhs WITH DataFlowPrivate#462ff392::Cached::TExprNode#ff ON FIRST 1 OUTPUT Lhs.1, Rhs.1

             1   ~0%    {1} r6 = JOIN r5 WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstArrayInclusionCall#::getAMaybeGuardedCapturedDef#0#f ON FIRST 1 OUTPUT Lhs.1

             7   ~0%    {1} r7 = JOIN r5 WITH DataFlowPublic#e1781e31::BarrierGuard#BarrierGuards#2462899b::stringConstCompare#::getAMaybeGuardedCapturedDef#0#f ON FIRST 1 OUTPUT Lhs.1

             8   ~0%    {1} r8 = r6 UNION r7
            65   ~2%    {1} r9 = r4 UNION r8
            98   ~1%    {1} r10 = r3 UNION r9
                        return r10
```

Author: hvitved

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPublic.qll

@@ -440,15 +440,24 @@ signature predicate guardChecksSig(CfgNodes::ExprCfgNode g, CfgNode e, boolean b
  * in data flow and taint tracking.
  */
 module BarrierGuard<guardChecksSig/3 guardChecks> {
+  pragma[nomagic]
+  private predicate guardChecksSsaDef(CfgNodes::ExprCfgNode g, boolean branch, Ssa::Definition def) {
+    guardChecks(g, def.getARead(), branch)
+  }
+
+  pragma[nomagic]
+  private predicate guardControlsSsaDef(
+    CfgNodes::ExprCfgNode g, boolean branch, Ssa::Definition def, Node n
+  ) {
+    def.getARead() = n.asExpr() and
+    guardControlsBlock(g, n.asExpr().getBasicBlock(), branch)
+  }
+
   /** Gets a node that is safely guarded by the given guard check. */
   Node getABarrierNode() {
-    exists(
-      CfgNodes::ExprCfgNode g, boolean branch, CfgNodes::ExprCfgNode testedNode, Ssa::Definition def
-    |
-      def.getARead() = testedNode and
-      def.getARead() = result.asExpr() and
-      guardChecks(g, testedNode, branch) and
-      guardControlsBlock(g, result.asExpr().getBasicBlock(), branch)
+    exists(CfgNodes::ExprCfgNode g, boolean branch, Ssa::Definition def |
+      guardChecksSsaDef(g, branch, def) and
+      guardControlsSsaDef(g, branch, def, result)
     )
     or
     result.asExpr() = getAMaybeGuardedCapturedDef().getARead()