Fix TypeLoadException exception error (#8157)

## Summary of changes

Fixes `TypeLoadException`[ being logged as an
error](https://app.datadoghq.com/error-tracking?query=service%3Ainstrumentation-telemetry-data%20%40lib_language%3Adotnet%20version%3A3.3%2A&et-side=activity&fromUser=false&issue_states=open&order=total_count&refresh_mode=sliding&source=all&sp=%5B%7B%22p%22%3A%7B%22issueId%22%3A%224cdd44b0-aea9-11f0-940c-da7ad0900002%22%7D%2C%22i%22%3A%22error-tracking-issue%22%7D%5D&from_ts=1769594245972&to_ts=1770199045972&live=true)
during tracer initialization on .NET Framework when
`System.Web.Hosting.HostingEnvironment` is unavailable.

## Reason for change

On .NET Framework 4.x, users were seeing this error during startup:

```
Error: Unable to get application name through ASP.NET settings
System.TypeLoadException
   at Datadog.Trace.PlatformHelpers.ApplicationNameHelpers.TryLoadAspNetSiteName(String& siteName)
   at Datadog.Trace.PlatformHelpers.ApplicationNameHelpers.GetApplicationName(TracerSettings settings)
```

## Root Cause

The existing code had a `try-catch` block inside `TryLoadAspNetSiteName`
to catch `TypeLoadException`, but the exception was thrown **during JIT
compilation** of the method, not during execution. When the JIT compiler
encountered `System.Web.Hosting.HostingEnvironment` references, it threw
`TypeLoadException` before any code in the method could execute - so the
inner catch block was never reached.

## Implementation details

Extracted the `System.Web`-dependent code into a separate method marked
with `[MethodImpl(MethodImplOptions.NoInlining)]`. This:

1. Defers JIT compilation of the System.Web-dependent code until the
method is actually called
2. Allows the `TypeLoadException` to be caught at the call site
3. Logs a **Warning** (expected behavior) instead of an **Error**

A similar pattern is already used in
`SecurityCoordinator.Framework.cs:243-244`.

## Test coverage

## Other details
<!-- Fixes #{issue} -->


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Author: NachoEchevarria

tracer/src/Datadog.Trace/PlatformHelpers/ApplicationNameHelpers.cs

@@ -8,6 +8,7 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using Datadog.Trace.Configuration;
 using Datadog.Trace.Logging;
 using Datadog.Trace.Util;
@@ -70,14 +71,10 @@ private static bool TryLoadAspNetSiteName([NotNullWhen(true)] out string? siteNa
 #if NETFRAMEWORK
         try
         {
-            // System.Web.dll is only available on .NET Framework
-            if (System.Web.Hosting.HostingEnvironment.IsHosted)
-            {
-                // if this app is an ASP.NET application, return "SiteName/ApplicationVirtualPath".
-                // note that ApplicationVirtualPath includes a leading slash.
-                siteName = (System.Web.Hosting.HostingEnvironment.SiteName + System.Web.Hosting.HostingEnvironment.ApplicationVirtualPath).TrimEnd('/');
-                return true;
-            }
+            // Call into a separate method to avoid TypeLoadException being thrown
+            // during JIT compilation of this method when System.Web types are unavailable.
+            // The NoInlining attribute ensures the JIT defers compilation until the call site.
+            return TryGetHostingEnvironmentSiteName(out siteName);
         }
         catch (TypeLoadException ex)
         {
@@ -87,4 +84,28 @@ private static bool TryLoadAspNetSiteName([NotNullWhen(true)] out string? siteNa
         siteName = null;
         return false;
     }
+
+#if NETFRAMEWORK
+    /// <summary>
+    /// This method must be called from within a try-catch block.
+    /// The TypeLoadException will be thrown at the CALLSITE when System.Web types are unavailable,
+    /// not inside this method, due to JIT compilation behavior.
+    /// The NoInlining attribute is critical to ensure this behavior.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static bool TryGetHostingEnvironmentSiteName([NotNullWhen(true)] out string? siteName)
+    {
+        // System.Web.dll is only available on .NET Framework
+        if (System.Web.Hosting.HostingEnvironment.IsHosted)
+        {
+            // if this app is an ASP.NET application, return "SiteName/ApplicationVirtualPath".
+            // note that ApplicationVirtualPath includes a leading slash.
+            siteName = (System.Web.Hosting.HostingEnvironment.SiteName + System.Web.Hosting.HostingEnvironment.ApplicationVirtualPath).TrimEnd('/');
+            return true;
+        }
+
+        siteName = null;
+        return false;
+    }
+#endif
 }