fix expr.qll and dbscheme merge issue

Author: Dilan Bhalla

csharp/ql/lib/semmle/code/csharp/exprs/internal/Expr.qll

@@ -0,0 +1,11 @@
+private import csharp
+
+pragma[nomagic]
+predicate isPatternExprDescendant(Expr e) {
+  e instanceof PatternExpr
+  or
+  exists(Expr parent |
+    isPatternExprDescendant(parent) and
+    e = parent.getAChildExpr()
+  )
+}