JIT: Relax cost improvement assert in 3-opt layout (#109835)

Follow-up to #109741. Fixes #109831. Fixes #109905. Fixes #109903.

Tolerate some floating-point imprecision when comparing the cost of a new layout produced by 3-opt to the previous layout's cost. The JitStress failures I looked all stressed JitOptRepeat, which can produce absurdly large loop block weights by rerunning optSetBlockWeights. Manually inspecting the layout decisions made for these methods shows 3-opt making reasonable transformations, but the assertion newLayoutCost < currLayoutCost fails due to imprecision from summing large block weights. Having a backup check that the layout costs are within some epsilon seems like a reasonable fix.

src/coreclr/jit/fgopt.cpp

@@ -5375,9 +5375,10 @@ bool Compiler::ThreeOptLayout::RunThreeOptPass(BasicBlock* startBlock, BasicBloc
         }
 
 #ifdef DEBUG
-        // Ensure the swap improved the overall layout
+        // Ensure the swap improved the overall layout. Tolerate some imprecision.
         const weight_t newLayoutCost = GetLayoutCost(startPos, endPos);
-        assert(newLayoutCost < currLayoutCost);
+        assert((newLayoutCost < currLayoutCost) ||
+               Compiler::fgProfileWeightsEqual(newLayoutCost, currLayoutCost, 0.001));
         currLayoutCost = newLayoutCost;
 #endif // DEBUG
     }