fix(TreeView): Fix invalid tree item children

[silvalaura]

Issue: none

What I did

MAST engineers reported a change in behavior from 4.6.0 to our prerelease. Items that had invalid children would get the expandable arrow when they shouldn't. In addition, I added unit tests so we don't break this accidentally in the future.

Screenshots:

All examples with the same code:

   <TreeView>
        <TreeItem label="Node 0 - fragment" itemId="item0" testId="item0">
          <></>
        </TreeItem>
        <TreeItem label="Node 1" itemId="item1" testId="item1">
          <TreeItem label="Child 1" itemId="item-child1">
            <TreeItem label="Grandchild 1" itemId="item-gchild1">
              <Tag>This is a tag as a child of Grandchild 1</Tag>
            </TreeItem>
          </TreeItem>
        </TreeItem>
        <TreeItem label="Node 2" itemId="item2">
          <TreeItem label="Child 2" itemId="item-child2">
            <TreeItem label="Grandchild 2" itemId="item-gchild2">
              <TreeItem label="Great-grandchild 2" itemId="item-ggchild2" />
              <TreeItem label="Great-grandchild 3" itemId="item-ggchild3" />
            </TreeItem>
          </TreeItem>
        </TreeItem>
        <TreeItem label="Node 3" itemId="item3"></TreeItem>
        <TreeItem label="Node 4" itemId="item4">
          Child of node 4 is just text
        </TreeItem>
      </TreeView>

In 4.6.0

In 4.7.0-next.50

Update from this PR

Checklist

• changeset has been added
• Pull request description is descriptive
• [-] I have made corresponding changes to the documentation
• New and existing unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

How to test

Open CodeSandbox and try different kinds of tree structures. Ensure that the items that are expandable are the expected ones (ones with valid children, whether that's a single TreeItem or multiple).

Note: to test previous behavior, open CS and change the package version from 4.6.0 to the latest prerelease

[changeset-bot]

🦋 Changeset detected

Latest commit: dbfccb5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
react-magma-dom	Patch

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[github-actions]

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[github-actions]

🚀 Deployed on https://storybook-preview-1584--upbeat-sinoussi-f675aa.netlify.app

[github-actions]

🚀 Deployed on https://docs-preview-1584--upbeat-sinoussi-f675aa.netlify.app

[github-actions]

🚀 Deployed on https://storybook-preview-1584--upbeat-sinoussi-f675aa.netlify.app

[moathabuhamad-cengage]

works as intended, tested locally on /story/treeview--invalid-tree-items

[silvalaura]

MAST engineers checked this version and are no longer seeing this visual issue.