Fix bug in OpenTelemetry SDK version validation code in StartupHook

[xiang17]

Why

Fixes a special case that #1692 didn't cover.

If the customer included the OpenTelemetry SDK with PackageReference in the csproj file but didn't have C# code calling OpenTelemetry APIs, the app will crash with a System.Reflection.TargetInvocationException which doesn't have the helpful System.NotSupportedException.

This is because Assembly.GetEntryAssembly()?.GetReferencedAssemblies()'s return value doesn't contain OpenTelemetry assembly unless it's invoked in C# code.

What

Rely on Type.GetType to check whether customer's app has dependency on OpenTelemetry.

Tests

Case 1

Add <PackageReference Include="OpenTelemetry" VersionOverride="1.4.0-rc.2" /> in the <ItemGroup> tag of examples\playground\AspNetCoreMvc\Examples.AspNetCoreMvc.csproj.

Unhandled exception. System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.NotSupportedException: Application has direct or indirect reference to older version of OpenTelemetry package 1.4.0.753.
   at StartupHook.ThrowIfReferenceIncorrectOpenTelemetryVersion(String loaderAssemblyLocation) in C:\c\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.AutoInstrumentation.StartupHook\StartupHook.cs:line 201
   at StartupHook.Initialize() in C:\c\opentelemetry-dotnet-instrumentation\src\OpenTelemetry.AutoInstrumentation.StartupHook\StartupHook.cs:line 70
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
   --- End of inner exception stack trace ---
   at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.StartupHookProvider.CallStartupHook(StartupHookNameOrPath startupHook)
   at System.StartupHookProvider.ProcessStartupHooks()

Case 2

examples\playground\AspNetCoreMvc\Examples.AspNetCoreMvc.csproj works fine.

Checklist

- [ ] CHANGELOG.md is updated.
- [ ] Documentation is updated.
- [ ] New features are covered by tests.