Expand System.Runtime.InteropServices.NFloat to support the APIs required by Xamarin

[tannergooding]

This resolves #63801.

Tests still need to be added.

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[tannergooding]

CC. @rolfbjarne, @marek-safar, @jeffhandley

[rolfbjarne]

Looks like two operators are reversed?

[stephentoub]

Nit: This description seems a bit misleading, as it tells you whether left is less than right but not whether right is strictly less then left.

Consider adopting the existing doc terminology that float/double use, e.g. "Returns a value that indicates whether a specified Double value is less than or equal to another specified Double value."

That goes for all these doc comments.

[tannergooding]

Consider adopting the existing doc terminology

I always forget that we have APIs exposed here that are functionally unavailable and will never be called 👍

I'll update this in a follow up PR as I need to also update IComparisonOperators and a few other places accordingly.

[stephentoub]

Gave it a quick skim and generally LGTM.

[tannergooding]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1774427144