net-standard testing and fixes

Proposed Changes

My testing of the net-standard branch was successful - I was able to dotnet build my project using the net-standard build of SQLProvider!

Fixed two broken in the DesignTime project to the new SSDT files
Upgraded to the latest version of Paket v5.257.0 in dotnet tools (I was having an issue building with net5 that were fixed in newer release)

Types of changes

What types of changes does your code introduce to SQLProvider? Put an x in the boxes that apply

[x] Bugfix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

[ ] Build and tests pass locally
[ ] I have added tests that prove my fix is effective or that my feature works (if appropriate)
[ ] I have added necessary documentation (if appropriate)

Further comments

This will be a huge deal for all the people unable to build with dotnet. Good job! Can you release this on nuget as a v2 "preview"?

fsprojects / SQLProvider