Rust: Fix bad join in unqualifiedPathLookup

Before
```
Pipeline standard for PathResolution::unqualifiedPathLookup/2#6b171b76#reorder_2_0_1@822d53wq was evaluated in 61 iterations totaling 118ms (delta sizes total: 131072).
          606491   ~0%    {4} r1 = SCAN `PathResolution::getASuccessor/3#febac7bd#prev_delta` OUTPUT In.1, In.2, In.0, In.3
          106457   ~1%    {3}    | JOIN WITH `PathResolution::unqualifiedPathLookup/4#e32cdfce_1230#join_rhs` ON FIRST 3 OUTPUT Lhs.3, Rhs.3, Lhs.1

          606491   ~2%    {4} r2 = SCAN `PathResolution::getASuccessor/3#febac7bd#prev_delta` OUTPUT In.0, In.2, In.3, In.1

           19261   ~0%    {4} r3 = JOIN r2 WITH `PathResolution::ModuleLikeNode.isRoot/0#dispred#21662e64` ON FIRST 1 OUTPUT Lhs.3, Lhs.0, Lhs.1, Lhs.2

        42776643   ~1%    {4} r4 = JOIN r2 WITH `doublyBoundedFastTC@PathResolution::hasChild/2#6b318d51#2@PathResolution::isRoot/1#a01ce5c3#1@PathResolution::hasCratePath/1#73ea688d#1` ON FIRST 1 OUTPUT Lhs.3, Rhs.1, Lhs.1, Lhs.2

        42795904   ~1%    {4} r5 = r3 UNION r4
           24921   ~6%    {3}    | JOIN WITH `PathResolution::RelevantPath.isCratePath/2#e595e892_120#join_rhs` ON FIRST 2 OUTPUT Lhs.3, Rhs.2, Lhs.2

          131378   ~2%    {3} r6 = r1 UNION r5
          131072   ~2%    {3}    | AND NOT `PathResolution::unqualifiedPathLookup/2#6b171b76#reorder_2_0_1#prev`(FIRST 3)
                          return r6
```

After
```
Pipeline standard for PathResolution::unqualifiedPathLookup/2#6b171b76#reorder_2_0_1@0553a4wi was evaluated in 66 iterations totaling 10ms (delta sizes total: 131072).
        610251  ~0%    {4} r1 = SCAN `PathResolution::getASuccessor/3#febac7bd#prev_delta` OUTPUT In.1, In.2, In.0, In.3
        131378  ~0%    {3}    | JOIN WITH `PathResolution::unqualifiedPathLookup1/4#781de0cd_1230#join_rhs` ON FIRST 3 OUTPUT Lhs.3, Rhs.3, Lhs.1
        131072  ~0%    {3}    | AND NOT `PathResolution::unqualifiedPathLookup/2#6b171b76#reorder_2_0_1#prev`(FIRST 3)
                       return r1
```

Author: hvitved

rust/ql/lib/codeql/rust/internal/PathResolution.qll

@@ -882,20 +882,24 @@ private predicate hasChild(ItemNode parent, ItemNode child) { child.getImmediate
 private predicate rootHasCratePathTc(ItemNode i1, ItemNode i2) =
   doublyBoundedFastTC(hasChild/2, isRoot/1, hasCratePath/1)(i1, i2)
 
+pragma[nomagic]
+private predicate unqualifiedPathLookup1(RelevantPath p, string name, Namespace ns, ItemNode encl) {
+  unqualifiedPathLookup(p, name, ns, encl)
+  or
+  // For `($)crate`, jump directly to the root module
+  exists(ItemNode i | p.isCratePath(name, i) |
+    encl.(ModuleLikeNode).isRoot() and
+    encl = i
+    or
+    rootHasCratePathTc(encl, i)
+  )
+}
+
 pragma[nomagic]
 private ItemNode unqualifiedPathLookup(RelevantPath path, Namespace ns) {
   exists(ItemNode encl, string name |
-    result = getASuccessor(encl, pragma[only_bind_into](name), ns)
-  |
-    unqualifiedPathLookup(path, name, ns, encl)
-    or
-    // For `($)crate`, jump directly to the root module
-    exists(ItemNode i | path.isCratePath(pragma[only_bind_into](name), i) |
-      encl.(ModuleLikeNode).isRoot() and
-      encl = i
-      or
-      rootHasCratePathTc(encl, i)
-    )
+    result = getASuccessor(encl, name, ns) and
+    unqualifiedPathLookup1(path, name, ns, encl)
   )
 }
 
@@ -916,8 +920,7 @@ private ItemNode resolvePath0(RelevantPath path, Namespace ns) {
   or
   exists(ItemNode q, string name |
     q = resolvePathQualifier(path, name) and
-    result = q.getASuccessor(name) and
-    ns = result.getNamespace()
+    result = getASuccessor(q, name, ns)
   )
   or
   result = resolveUseTreeListItem(_, _, path) and