[DRAFT] Feature #15136: Implement amazon-style navigation triangle

[prodoelmit]

Resolves: #15136

Implements amazon-style navigation triangle.

There are several tricky behaviors to handle. The current state of pull request needs a lot of cleanup, so it's mostly intended for demo purposes.

• I signed the CLA
• The title of the PR describes the problem it addresses
• Each commit's message describes its purpose and effects, and references the issue it resolves
• If changes are extensive, there is a sequence of easily reviewable commits
• The code in the PR follows the coding rules
• There are no unnecessary changes
• The code compiles and runs on my machine, preferably after each commit individually
• I created a unit test or vtest to verify the changes I made (if applicable)