Update type check for TreeContainerProps

[colin-grant-work]

What it does

The previous implementation of the check to distinguish TreeProps from TreeContainerProps could be confused by the fact that both had a search key. This PR introduces special handling of that field to ensure that the check returns the correct value.

How to test

1. Assert that the new test introduced in this PR passes.
2. use createTreeContainer with TreeProps that include a search field. Observe that the tree view is successfully constructed and functions correctly.

e.g. in outline-view-frontend-module.ts replace this:

    const child = createTreeContainer(parent, {
         props: { expandOnlyOnExpansionToggleClick: true, search: true },
         widget: OutlineViewWidget,
         model: OutlineViewTreeModel,
         decoratorService: OutlineDecoratorService,
     });

with this:

    const child = createTreeContainer(parent, { ...defaultTreeProps, expandOnlyOnExpansionToggleClick: true, search: true });


     child.unbind(TreeWidget);
     child.bind(OutlineViewWidget).toSelf();

     child.unbind(TreeModelImpl);
     child.bind(OutlineViewTreeModel).toSelf();
     child.rebind(TreeModel).toService(OutlineViewTreeModel);

     child.bind(OutlineDecoratorService).toSelf().inSingletonScope();
     child.rebind(TreeDecoratorService).toDynamicValue(ctx => ctx.container.get(OutlineDecoratorService)).inSingletonScope();

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I confirmed with the changes that the outline-view can successfully be constructed and viewed (the search does not work, but it does without the changes to the outline-view itself).

[vince-fugnitto]

The changes look good to me 👍
I confirmed that the new code works well, the outline-view works including the snippet, and so does searching in the trees.

[vince-fugnitto]

minor: add a newline after the header.