Fix x86 async frame generic type resolution in DBI (#126915)

CordbAsyncFrame::LoadGenericArgs was using SafeReadStruct<CORDB_ADDRESS>
to read the generic arg token from the continuation object.
CORDB_ADDRESS is ULONG64 (always 8 bytes), but on x86 targets the field
is a 4-byte pointer. Reading 8 bytes pulled in adjacent memory,
producing garbage pointer values that caused EnumerateTypeParameters to
return E_INVALIDARG.

Changed to SafeReadStruct<SIZE_T> which matches the target pointer size
(4 bytes on x86, 8 bytes on x64), consistent with how
CordbJITILFrame::LoadGenericArgs reads tokens via
GetRegisterOrStackValue.

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

src/coreclr/debug/di/rsthread.cpp

@@ -11546,8 +11546,14 @@ void CordbAsyncFrame::LoadGenericArgs()
         {
             if (m_asyncVars[i].ilVarNum == genericArgIndex)
             {
-
-                HRESULT hr = GetProcess()->SafeReadStruct(m_continuationAddress + m_asyncVars[i].offset, &genericTypeParam);
+                // Read a target-pointer-sized value. CORDB_ADDRESS is always 8 bytes (ULONG64),
+                // but on x86 targets the generic arg field is only a 4-byte pointer. Using
+                // SIZE_T (which is pointer-sized for the DBI build, matching the target here)
+                // avoids reading adjacent memory. This mirrors how CordbJITILFrame::Init()
+                // reads the raw token via GetRegisterOrStackValue (which returns SIZE_T).
+                SIZE_T rawToken = 0;
+                HRESULT hr = GetProcess()->SafeReadStruct(m_continuationAddress + m_asyncVars[i].offset, &rawToken);
+                genericTypeParam = (CORDB_ADDRESS)rawToken;
                 IfFailThrow(hr);
                 break;
             }