Move to dib extension

[WhiteBlackGoose]

#474

[WhiteBlackGoose]

seems like dotnet/interactive#1808 is still hitting

[Rafael-SOWNet]

Done on master, by another route. Sources/AngouriMath/extension.dib exists and is packed into the NuGet package:

<None Include="extension.dib" Pack="true" PackagePath="interactive-extensions/dotnet" />

so installing AngouriMath alone loads LaTeX rendering in a notebook, without AngouriMath.Interactive
— which is what this branch was for. The What's new entry for 1.4-preview.4 records it landing.

Closing as achieved rather than abandoned. The branch itself is four years behind a master whose
directory layout has since changed (f0db3eef moved the library up a folder), so there is nothing to
rebase onto.