[wasm] Fix tests skipped, or not discovered due to trimming

`InlineDataDiscoverer`, and `MemberDataDiscoverer` were getting
trimmed, which would cause some tests to get skipped. For example, ~9k
tests in `System.Data.Common.Tests`

Author: radical

eng/testing/ILLink.Descriptor.xunit.xml

@@ -12,6 +12,7 @@
   <assembly fullname="Microsoft.DotNet.XUnitExtensions" />
   <assembly fullname="xunit.core">
     <namespace fullname="Xunit" />
+    <namespace fullname="Xunit.Sdk" />
   </assembly>
   <assembly fullname="xunit.runner.utility.netcoreapp10" />
 </linker>