Fix broken snippet completion after itemDefault implementation

[JessicaJHee]

Fixes #2560

[rgrunber]

So basically, we just forgot to set the new textEditText (required for the defaultItems feature) for snippets ?

What about JavadocCompletionProposal ? I don't see it here but definitely called at https://github.com/eclipse/eclipse.jdt.ls/blob/335ad830a64e04c8ef4d633203c72c777dea84e8/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/CompletionHandler.java#L228 . It doesn't set a text edit, but in the absence of one, the label itself is used.

[JessicaJHee]

I believe because we set the textEdit here:

https://github.com/eclipse/eclipse.jdt.ls/blob/335ad830a64e04c8ef4d633203c72c777dea84e8/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/contentassist/JavadocCompletionProposal.java#L114

We don't need to handle this case because it will prioritize the use of textEdit and not insertText. (https://code.visualstudio.com/api/references/vscode-api#CompletionItem) The problem with the other cases is that we let the client side handle the completion with insertText since we don't set textEdit.

[rgrunber]

Ok, and the snippets don't seem to ever set a text edit so we never have to worry about that. They just set insertText, which is fine, because that can co-exist with textEditText just like it does for non-snippet items.

[fbricon]

Can we have some unit test showcasing the fix fixes the issue? Testing something like

public class Foo {
    void sysop(){}
    
    public static void main(Object[]...args) {
        new Foo().syso| //should return 2 completion items: sysop() and sysout postfix
    }
}

[fbricon]

Thanks @JessicaJHee!