[Example App] implement more complex layout for grid view

[jessesquires]

Some ideas:

• Orthogonal sections (Horizontally scrolling sections)
• Groups
• Search/Filter (add a search bar and filter results, see Implementing Modern Collection Views below)

Maybe? Eventually?

• Collapsing headers (see [DataSource] Support section expanding and collapsing #33)
• Layout changes? (see Allow changing layouts? #92)

⚠️ No need to do this all at once. Small PRs with one new feature are best. 😊

Examples and Sample code:

• Implementing Modern Collection Views
• Updating Collection Views Using Diffable Data Sources
• Getting Started with UI​Collection​View​Compositional​Layout