improvement: resolve project app names set using a module attribute

[zachallaun]

This PR also fixes two bugs in Common.expand_literal/1. Previously, the following would be returned:

iex(1)> ":foo" |> Sourceror.parse_string!() |> Sourceror.Zipper.zip() |> Igniter.Code.Common.expand_literal()
{:ok, {:__block__, [trailing_comments: [], leading_comments: [], line: 1, column: 1], [:foo]}}
iex(2)> "@foo" |> Sourceror.parse_string!() |> Sourceror.Zipper.zip() |> Igniter.Code.Common.expand_literal()
{:ok,
 {:@, [trailing_comments: [], leading_comments: [], line: 1, column: 1],
  [{:foo, [trailing_comments: [], leading_comments: [], line: 1, column: 2], nil}]}}

With this PR:

iex(1)> ":foo" |> Sourceror.parse_string!() |> Sourceror.Zipper.zip() |> Igniter.Code.Common.expand_literal()
{:ok, :foo}
iex(2)> "@foo" |> Sourceror.parse_string!() |> Sourceror.Zipper.zip() |> Igniter.Code.Common.expand_literal()
:error

Contributor checklist

• Bug fixes include regression tests
• Features include unit/acceptance tests

[zachdaniel]

Looking great. One small question added. Also curious if you'd rather get the other one in before this.

[zachdaniel]

We can ignore the CI issue, that is a misconfiguration in our CI that I need to address.

[zachallaun]

Marked as a draft for now because this PR now relies on #113, which hasn't been merged yet, so tests are now failing. Once it's merged, I'll rebase and mark as ready for review.

Edit: Done 🙂