feature: Add missing case patterns

[ghostbuster91]

related to scalameta/metals-feature-requests#350

[ghostbuster91]

The test fails for now because the Leaf case is added in wrong place.
The current output is:

Leaf(_) match {
  case Node(_, _) => ???
}

My idea is to create something like AutoImportProvider where I would get access to the typedTree and more importantly its parent, which in our case is

tree match {
  case Node(_, _) => ???
}

I could then use the endRange of such tree, and insert the missing cases just one line before it. This would involve going through the presentation compiler interface.

Though maybe there is a simpler way. Let me know what you think.
Eventually I could try to use

      name <- trees
        .findLastEnclosingAt[Term.Name](path, params.getRange().getStart())

but that gives the parent of the whole match, which seems to be too much.

[kasiaMarek]

I think untyped trees should be enough here. I'm not sure what you mean by "the parent of the whole match". The whole match should be a Term.Match. Using that you should be able to find the last case and place new ones after it. Here you can explore the syntax trees: https://astexplorer.net.

[ghostbuster91]

By "parent of the whole match" I meant that I was getting:

def method(tree: Tree) = {
   tree match {
     case Node(_, _) => ???
     case Leaf(_) => ???
   }
 }

but I must have had something wrong because now it works as expected. Thanks 👍

[ghostbuster91]

Closing in favor of scala/scala3#18314