Parameterize directories used by dotnet-ef

[natemcmaster]

Fix #5311 by adding back --startup-project.

NB: using --startup-project requires that "Microsoft.EntityFrameworkCore.Design" be installed startup project, not the current project. This partially enables class libraries. cref #5320

TODO: parameter order on command line still matters, so this option must be added between "ef" and the next sub command. E.g. dotnet ef --startup-project ../WebApp1 database update. This is already tracked in #5188

This is built under the assumption that on .NET Core CLI, the current working directory is your target project, and is not necessarily the startup project. The reverse assumption (that dotnet-ef should always be executed on startup) is not consistent with other .NET Core CLI commands that alter files.

Worth noting: we are still using relative project directories as the value of --startup-project. This is to stay consistent with how .NET Core CLI handles preferences to projects. (Example see dotnet run --help)

cc @bricelam @divega @rowanmiller

[natemcmaster]

(PS, before I request ask-mode approval, let's consider first that this is the behavior we want.)

[bricelam]

Wonderful! It's exactly how I always wanted it to work.

[bricelam]

This isn't ASP.NET-specific. Maybe something like "...base directory for the application."

[natemcmaster]

Can we drop the data directory and merge them into one parameter? I can't think of a scenario in which data directory is different from the app base path.

[bricelam]

Classic ASP.NET uses <base>/App_Data

[bricelam]

But yes, it's probably OK to do that for now on CLI.

[natemcmaster]

I think I'm going to leave it, as long as there is the possible scenario that data directory may not be the app base path.

[bricelam]