[clr-ios] Preserve inherited MemberData statics on maccatalyst CoreCLR (#128409)

## Description

On maccatalyst-arm64 `AllSubsets_CoreCLR`, ILLink strips the inherited
`ReadWrite_Success_MemberData` and
`CopyToAsync_AllDataCopied_MemberData` statics on
`ConnectedStreamConformanceTests`, so xUnit's `[MemberData]` lookup
fails for `CryptoStreamTests.ReadWrite_Success` and
`NetworkStreamTest.CopyToAsync_AllDataCopied`. Adds a
`[DynamicDependency]` on each derived override to root the base statics,
and restores the `IsMultithreadingSupported` guard on
`CopyToAsync_AllDataCopied`.

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: kotlarmilos <kotlarmilos@users.noreply.github.com>

Author: kotlarmilos

src/libraries/System.Net.Sockets/tests/FunctionalTests/ILLink.Descriptors.xml

@@ -0,0 +1,3 @@
+<linker>
+  <assembly fullname="StreamConformanceTests" />
+</linker>

src/libraries/System.Net.Sockets/tests/FunctionalTests/System.Net.Sockets.Tests.csproj

@@ -114,5 +114,6 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CommonTestPath)StreamConformanceTests\StreamConformanceTests.csproj" />
+    <TrimmerRootDescriptor Condition="'$(TargetsAppleMobile)' == 'true' and '$(EnableAggressiveTrimming)' == 'true' and '$(UseNativeAotRuntime)' != 'true'" Include="$(MSBuildThisFileDirectory)ILLink.Descriptors.xml" />
   </ItemGroup>
 </Project>

src/libraries/System.Security.Cryptography/tests/ILLink.Descriptors.xml

@@ -0,0 +1,3 @@
+<linker>
+  <assembly fullname="StreamConformanceTests" />
+</linker>

src/libraries/System.Security.Cryptography/tests/System.Security.Cryptography.Tests.csproj

@@ -872,6 +872,7 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(CommonTestPath)StreamConformanceTests\StreamConformanceTests.csproj" />
+    <TrimmerRootDescriptor Condition="'$(TargetsAppleMobile)' == 'true' and '$(EnableAggressiveTrimming)' == 'true' and '$(UseNativeAotRuntime)' != 'true'" Include="$(MSBuildThisFileDirectory)ILLink.Descriptors.xml" />
     <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Cryptography.Pkcs\src\System.Security.Cryptography.Pkcs.csproj" />
     <PackageReference Include="System.Security.Cryptography.X509Certificates.TestData" Version="$(SystemSecurityCryptographyX509CertificatesTestDataVersion)" />
     <!-- Reference the `NetCoreAppMinimum` build which has a functional BinaryFormatter and force a private copy to ensure it's not excluded -->