Pkg.jl: Ability to pass `test_args` when using `] test MyPackage` in the REPL mode [Feature Request]

[DilumAluthge]

I can pass arguments to the test process by using the test_args keyword argument to Pkg.test. See https://github.com/JuliaLang/Pkg.jl/pull/1226 and https://github.com/JuliaLang/Pkg.jl/pull/1688 for more details.

Currently, there is no way to pass test_args when using the REPL mode, i.e. when doing ] test MyPackage.

It would be really convenient to be able to do so.

[DilumAluthge]

cc: @00vareladavid

[DilumAluthge]

@fredrikekre suggested in https://github.com/JuliaLang/Pkg.jl/pull/1226#issuecomment-503426739 that we probably only need to add support for passing test_args in the REPL mode, since julia_args will not be used very often.

[00vareladavid]

I think it is a good idea. I think Fredrik's proposed syntax pkg> test Example -- arg1 arg2 is good for this. We will have to adjust the REPL parsing a bit for this to work though