fix: Stop warnings from showing in Blazor WASM projects (#4519)

Fix WASM0001 warnings when building Blazor WebAssembly projects that came out from our native bindings.

The fix was to change the way we represent `sentry_value_t` in C# side, instead of using `FieldOffset`, we use a backing field along with getters and setters for the variable as a `double`, or `ulong`.

Fixes #3369

Author: alexsohn1126

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Upload linked PDBs to fix non-IL-stripped symbolication for iOS ([#4527](https://github.com/getsentry/sentry-dotnet/pull/4527))
 - In MAUI Android apps, generate and inject UUID to APK and upload ProGuard mapping to Sentry with the UUID ([#4532](https://github.com/getsentry/sentry-dotnet/pull/4532))
+- Fixed WASM0001 warning when building Blazor WebAssembly projects ([#4519](https://github.com/getsentry/sentry-dotnet/pull/4519))
 
 ## 5.15.1
 

src/Sentry/Platforms/Native/CFunctions.cs

@@ -322,14 +322,25 @@ private static Dictionary<long, DebugImage> LoadDebugImagesOnce(IDiagnosticLogge
     [DllImport("sentry-native")]
     internal static extern void sentry_value_decref(sentry_value_t value);
 
-    // native union sentry_value_u/t
-    [StructLayout(LayoutKind.Explicit)]
+    // Mirrors the native `sentry_value_t` union (uint64_t or double).
+    // Implemented with a single ulong backing field and BitConverter
+    // to reinterpret values, since explicit unions cause issues with
+    // Blazor WASM interop generators.
     internal struct sentry_value_t
     {
-        [FieldOffset(0)]
-        internal ulong _bits;
-        [FieldOffset(0)]
-        internal double _double;
+        private ulong _bits;
+
+        internal ulong Bits
+        {
+            readonly get => _bits;
+            set => _bits = value;
+        }
+
+        internal double Double
+        {
+            readonly get => BitConverter.UInt64BitsToDouble(_bits);
+            set => _bits = BitConverter.DoubleToUInt64Bits(value);
+        }
     }
 
     [DllImport("sentry-native")]