Examples: move code into `src` directory

Doing so would enable anyone to quickly import a particular example on https://codesandbox.io/s/github, and play around with it.

Inspect the repository's example code and current directory structure, then identify which examples need to move into a src directory. Verify the resulting layout supports importing an individual example through the linked CodeSandbox GitHub flow; completion means the examples are relocated and remain usable there.

Written by the indexing model from the issue text.