Move Font*, Image* and Margins converters to System.Drawing.Common and apply Unit and Name converter

[safern]

Fixes: #33061
Fixes: #1011

cc: @DustinCampbell @merriemcgaw @RussKie

@Anipik I'm using the old Generate PNSE exclude API list attribute here.

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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.

[safern]

Touching ref assemblies but not adding new API.

[eerhardt]

<TargetFrameworks>$(NetCoreAppCurrent);netcoreapp3.0</TargetFrameworks>

This project still builds for netcoreapp3.0. Do we need to handle this specially?

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Refers to: src/libraries/System.Windows.Extensions/ref/System.Windows.Extensions.csproj:3 in 8554791. [](commit_id = 8554791, deletion_comment = False)

[safern]

This project still builds for netcoreapp3.0. Do we need to handle this specially?

Not really because it is not part of the shared framework and the typeforwards are yo System.Drawing.Common which will be in the netcoreapp3.0 implementation as well which is not inbox either, so it will have a PackageReference to System.Drawing.Common so it would work fine.