chore: inst/shiny -> inst/examples-shiny

[gadenbuie]

Moves the new, non-legacy shiny examples from inst/shiny to inst/examples-shiny.

See prior discussions in #3907

[cpsievert]

I'm pretty sure @schloerke wants it to be inst/{package}

[gadenbuie]

I'm pretty sure @schloerke wants it to be inst/{package}

Oh, from #3907 it sounded like a fixed inst/shiny was the recommendation and in #3917 Karan implemented it as inst/shiny-examples.

I feel pretty strongly that we should use a clear, unambiguous and likely unique directory name for the purpose of shiny::runExample() and that inst/examples-shiny fits that bill.