Add --file and --startup-file options to dotnet-ef

[AndriySvyryd]

See #38157
This will align with dotnet run

TBD: whether they are synonyms for --project and --startup-project or completely disjoint

[roji]

Design decision: have --file and --project be synonymous, like dotnet build but not like dotnet run.

@AndriySvyryd does this belong on the dotnet run board?

[AndriySvyryd]

@AndriySvyryd does this belong on the dotnet run board?

That depends on whether @jjonescz wants to (re)do this work.

[jjonescz]

I can create a PR for this.