Move API docs for new APIs into <remarks> (rather than summary)

[natke]

Problem seen here:

• See: https://review.docs.microsoft.com/en-us/dotnet/api/microsoft.ml.transforms?view=ml-dotnet&branch=smoke-test
• https://review.docs.microsoft.com/en-us/dotnet/api/microsoft.ml.data?view=ml-dotnet&branch=smoke-test

Includes docs for these components

• https://review.docs.microsoft.com/en-us/dotnet/api/microsoft.ml.data.svmlightloader?view=ml-dotnet&branch=smoke-test
• https://review.docs.microsoft.com/en-us/dotnet/api/microsoft.ml.transforms.expressionestimator?view=ml-dotnet&branch=smoke-test

All of the docs are in the summary element, which renders too much information on the summary page. If we move most of it into the remarks section, then this will be fixed.