Completion suggestions for arrays, integers suggest ${} placeholders

Summary

More of a question than a bug report.

We have a JSONSchema that encodes various values like:

          "aliases" : {
            "type" : "array",
            "items" : {
              "type" : "string"
            }
          },

The yaml-language-server provides a completion that is like:

aliases:
  - ${1:""}

Similarly, we've noticed that integer values like:

          "display_order" : {
            "type" : "integer"
          },

which suggests:

display_order: ${1:0}

Why are these the suggested defaults? I read through the code and it looks intentional. That is, it all happens in code that understands it's generating a suggestion for an array value or an integer value.

I double checked the yaml syntax and don't believe this is a standard array format which left me more confused.

I'm happy to open a PR with a patch, but given how long the implementation has existed in the code, I wanted to check first.

I believe this issue may be related, in that when I first hit the problem, I was trying to find a way to insert an array literal as the suggestion: https://github.com/redhat-developer/yaml-language-server/issues/409

Start by inspecting the completion-generation code for array and integer values, which the report says intentionally produces these placeholders. Compare the behavior with the related issue 409 and establish the expected YAML completion format before making a change; done means the default suggestions match that expected format and are covered by the relevant completion tests.