Rust: Add documentation and type inference for CfgPredExpr and CfgPredPat

rust/ql/lib/codeql/rust/controlflow/internal/ControlFlowGraphImpl.qll

@@ -380,6 +380,8 @@ module ExprTrees {
 
   class LiteralExprTree extends LeafTree instanceof LiteralExpr { }
 
+  class CfgPredExprTree extends LeafTree instanceof CfgPredExpr { }
+
   abstract class LoopingExprTree extends PostOrderTree {
     override predicate propagatesAbnormal(AstNode child) { child = this.getLoopBody() }
 
@@ -630,6 +632,8 @@ module PatternTrees {
 
   class RestPatTree extends LeafTree, RestPat { }
 
+  class CfgPredPatTree extends LeafTree, CfgPredPat { }
+
   class LiteralPatTree extends StandardPostOrderTree, LiteralPat {
     override AstNode getChildNode(int i) { i = 0 and result = this.getLiteral() }
   }

rust/ql/lib/codeql/rust/internal/typeinference/TypeInference.qll

@@ -3119,6 +3119,10 @@ private module Input3 implements InputSig3 {
   Type inferTypeCertainLanguageSpecific(AstNode n, TypePath path) {
     result = inferLiteralType(n, path, true)
     or
+    (n instanceof CfgPredExpr or n instanceof CfgPredPat) and
+    path.isEmpty() and
+    result instanceof BoolType
+    or
     result = inferRefPatType(n) and
     path.isEmpty()
     or