Remove some uses of dynamic from HardwareIntrinsic test code (#118273)

This is preventing the AdvSimd tests from running in NativeAOT contexts.

Fixes #118234

Author: snickolls-arm

src/tests/JIT/HardwareIntrinsics/Arm/AdvSimd/AdvSimd_r.csproj

@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <!-- https://github.com/dotnet/runtime/issues/118234 -->
-    <NativeAotIncompatible>true</NativeAotIncompatible>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>Embedded</DebugType>

src/tests/JIT/HardwareIntrinsics/Arm/AdvSimd/AdvSimd_ro.csproj

@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <!-- https://github.com/dotnet/runtime/issues/118234 -->
-    <NativeAotIncompatible>true</NativeAotIncompatible>
   </PropertyGroup>
   <PropertyGroup>
     <DebugType>Embedded</DebugType>

src/tests/JIT/HardwareIntrinsics/Arm/Shared/Helpers.cs

@@ -7789,35 +7789,33 @@ public static W MultiplyAddWidening<W, N>(W op1, N op2, N op3)
             where W : IBinaryInteger<W>
             where N : IBinaryInteger<N>
         {
-            dynamic a = op2;
-            dynamic b = op3;
-            W product = (W)((W)a * (W)b);
-            W r = (W)(op1 + product);
-            return r;
+            W a = W.CreateChecked(op2);
+            W b = W.CreateChecked(op3);
+            W product = W.CreateTruncating(a * b);
+            return W.CreateTruncating(op1 + product);
         }
 
         public static W MultiplySubtractWidening<W, N>(W op1, N op2, N op3)
             where W : IBinaryInteger<W>
             where N : IBinaryInteger<N>
         {
-            dynamic a = op2;
-            dynamic b = op3;
-            W product = (W)((W)a * (W)b);
-            W r = (W)(op1 - product);
-            return r;
+            W a = W.CreateChecked(op2);
+            W b = W.CreateChecked(op3);
+            W product = W.CreateTruncating(a * b);
+            return W.CreateTruncating(op1 - product);
         }
 
         public static N AddRoundedHighNarrowing<W, N>(W op1, W op2)
             where W : IBinaryInteger<W>
             where N : IBinaryInteger<N>
         {
             int halfsize = default(N).GetByteCount() * 8;
-            dynamic a = op1;
-            dynamic b = op2;
-            ulong sum = (ulong)a + (ulong)b;
+            ulong a = ulong.CreateChecked(op1);
+            ulong b = ulong.CreateChecked(op2);
+            ulong sum = a + b;
             ulong bias = 1UL << (halfsize - 1);
-            dynamic result = sum + bias;
-            return (N)(result >> halfsize);
+            ulong result = (sum + bias) >> halfsize;
+            return N.CreateTruncating(result);
         }
 
         public static N AddRoundedHighNarrowingEven<W, N>(W op1, W op2, int i)
@@ -7839,12 +7837,12 @@ public static N SubtractRoundedHighNarrowing<W, N>(W op1, W op2)
             where N : IBinaryInteger<N>
         {
             int halfsize = default(N).GetByteCount() * 8;
-            dynamic a = op1;
-            dynamic b = op2;
+            ulong a = ulong.CreateChecked(op1);
+            ulong b = ulong.CreateChecked(op2);
             ulong sum = (ulong)a - (ulong)b;
             ulong bias = 1UL << (halfsize - 1);
-            dynamic result = sum + bias;
-            return (N)(result >> halfsize);
+            ulong result = (sum + bias) >> halfsize;
+            return N.CreateTruncating(result);
         }
 
         public static N SubtractRoundedHighNarrowingEven<W, N>(W op1, W op2, int i)