Allow disambiguation when two packages expose modules with the same name

[evancz]

People have ran into cases where two different packages expose modules with the same name. Reported examples include:

• Date.Format from mgold/elm-date-format and rluiten/elm-date-extra in Module name collision in generated code #826 (comment)
• Animation from mdgriffith/elm-style-animation and mgold/elm-animation in When two packages use the same Module.Name, neither can be used. elm-lang/elm-package#257
• Element from evancz/elm-graphics and mdgriffith/style-elements in Can't compile when multiple packages export same name modules #1626
• Validate from local module and rtfeldman/elm-validate in Package name collisions #1043
• Memo from jvoigtlaender/elm-memo and ktonon/elm-memo-pure for benchmarking in Module name collisions of this and external packages #1628
• Mouse from elm-lang/mouse and mpizenberg/elm-pointer-events for handling mouse events Mouse.clicks mpizenberg/elm-pointer-events#9

In some of these cases, I do not understand why folks are using two packages for the same thing. The Element case is the best one in my opinion, even though it seems quite unlikely. It makes sense that they both use that name and have different goals. Should they end up in the same project though? Less clear. Also, when you have a local module, you can always choose a different name.

If you have other examples, open a new issue. Just give the error and reference this issue.

Design considerations include:

• Should it be easy to use two packages that claim to solve the same problem? Seems bad.
• Will people do silly module renaming to work around this? Not observed so far, but would be bad to end up with silly names or "conventions" to subvert the previous design consideration.
• Can the syntax really be nice enough to ensure that "conventions" do not arise anyway?