Update lpFirst and lpTop to reflect accurate compacted blocks (#51033)

* include first and top in compacting

* Convert to assert

* Revert "Convert to assert"

This reverts commit 7da1a8c7d910ad00bbc7b40314997f70960729a5.

src/coreclr/jit/fgopt.cpp

@@ -1996,6 +1996,20 @@ void Compiler::fgUpdateLoopsAfterCompacting(BasicBlock* block, BasicBlock* bNext
         {
             optLoopTable[loopNum].lpEntry = block;
         }
+
+        /* Check the loop's first block */
+
+        if (optLoopTable[loopNum].lpFirst == bNext)
+        {
+            optLoopTable[loopNum].lpFirst = block;
+        }
+
+        /* Check the loop top */
+
+        if (optLoopTable[loopNum].lpTop == bNext)
+        {
+            optLoopTable[loopNum].lpTop = block;
+        }
     }
 }