Merge pull request github#14098 from hvitved/csharp/cil-best-impl

C#: Speedup `bestImplementation`

Author: hvitved

csharp/ql/lib/semmle/code/cil/Stubs.qll

@@ -32,12 +32,12 @@ private module Cached {
     exists(Assembly asm |
       asm = mi.getLocation() and
       (assemblyIsStubImpl(asm) implies asm.getFile().extractedQlTest()) and
-      not exists(MethodImplementation better | mi.getMethod() = better.getMethod() |
-        mi.getNumberOfInstructions() < better.getNumberOfInstructions()
-        or
-        mi.getNumberOfInstructions() = better.getNumberOfInstructions() and
-        asm.getFile().toString() > better.getLocation().getFile().toString()
-      ) and
+      mi =
+        max(MethodImplementation impl |
+          mi.getMethod() = impl.getMethod()
+        |
+          impl order by impl.getNumberOfInstructions(), impl.getLocation().getFile().toString() desc
+        ) and
       exists(mi.getAnInstruction())
     )
   }