Some markdown-formatted remarks are ported into triple slash comments with invalid structure

Compare the source MemoryManager`1.xml remarks with the resulting MemoryManager.cs triple-slash comments shown in the issue. Trace the documentation-porting path that handles the remarks and format elements, then verify that the generated remarks have valid structure without duplicated content.

As seen in MemoryManager<T> from System.Memory in dotnet/runtime, some <remarks> sections are getting produced with invalid structure, and duplicated content.

From `MemoryManager`1.xml`

  <Docs>
    <typeparam name="T">The type of items in the memory buffer managed by this memory manager.</typeparam>
    <summary>An abstract base class that is used to replace the implementation of <see cref="T:System.Memory`1" />.</summary>
    <remarks>
      <format type="text/markdown"><![CDATA[  

The `MemoryManager<T>` class is used to extend the knowledge of types that <xref:System.Memory%601> is able to represent. For example, you can derive from `MemoryManager<T>` to allow <xref:System.Memory%601> to be backed by a <xref:System.Runtime.InteropServices.SafeHandle>.

> [!NOTE]
> The `MemoryManager<T>` class is intended for advanced scenarios. Most developers do not need to use it.

       ]]></format>
    </remarks>
  </Docs>

Before porting the docs into triple slash comments, this was the content of MemoryManager.cs:

    /// <summary>
    /// Manager of <see cref="System.Memory{T}"/> that provides the implementation.
    /// </summary>
    public abstract class MemoryManager<T> : IMemoryOwner<T>, IPinnable

After porting, this is the result:

    /// <summary>An abstract base class that is used to replace the implementation of <see cref="System.Memory{T}" />.</summary>
    /// <typeparam name="T">The type of items in the memory buffer managed by this memory manager.</typeparam>
    /// <remarks>The `MemoryManager<T>` class is used to extend the knowledge of types that <see cref="System.Memory{T}" /> is able to represent. For example, you can derive from `MemoryManager<T>` to allow <see cref="System.Memory{T}" /> to be backed by a <see cref="System.Runtime.InteropServices.SafeHandle" />.
    /// <format type="text/markdown"><![CDATA[
    /// > [!NOTE]
    /// > The `MemoryManager<T>` class is intended for advanced scenarios. Most developers do not need to use it.
    /// ]]></format></remarks>
    public abstract class MemoryManager<T> : IMemoryOwner<T>, IPinnable

The <remarks> section has the content duplicated, once inside the <format> and once before it, which is an invalid structure.