Controls: Fix UI to add array items

[sookmax]

Closes #22903

What I did

I applied the same style to .rejt-array-node > span > * as .rejt-object-node > span > *

The bug was caused by the plus button being not clickable because it is obscured by the pseudo element in the same level (.rejt-not-collapsed::before), which is absolutely positioned with z-index 1. So by applying position: relative and z-index: 2 to the selector .rejt-array-node > span > *, the plus button can now be interacted if the object is an array as well.

How to test

1. Run a sandbox for template, e.g. yarn task --task sandbox --start-from auto --template react-vite/default-ts
2. Add some test array to the primary story in sandbox/react-vite-default-ts/src/stories/Button.stories.ts

// More on writing stories with args: https://storybook.js.org/docs/react/writing-stories/args
export const Primary: Story = {
  args: {
    primary: true,
    label: 'Button',
    array: [{
      a: 1,
      b: "2",
      c: false
    }, {
      a: 2,
      b: "3",
      c: true
    }]
  },
};

3. Go over to Controls panel for Primary story and look for array field.
4. Interact with the plus button in the first line and see if it works.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[yannbf]

Thank you so much for your contribution @sookmax <3