Add sustainEnvAndQuoted(). Remove getQuosure()

[schloerke]

Related: #3462
Related: #3466

exprToFunction() (and installExprFunction()) do not work in all situations and reaching up into the calling code is dangerous / should be avoided. Now, the dangerous code is isolated to sustainEnvAndQuoted(), which ideally package authors will stop using.

With the updated code, all handling will be done with quosures. woot.

---

Shiny 1.6.0 code

renderDouble <- function(expr, env = parent.frame(), quoted = FALSE) {
	func <- exprToFunction(expr, env, quoted)
	function() {
		rep(func(), 2)
	}
}

Shiny 1.7.0 migration code

renderDouble <- function(expr, env = deprecated(), quoted = deprecated()) {
	q <- enquo0(expr)
	q <- sustainEnvAndQuoted(q, expr, env, quoted)
    func <- quoToFunction(q)
	function() {
		rep(func(), 2)
	}
}

Ideal Shiny 1.7.0 code

renderDouble <- function(expr) {
    func <- quoToFunction(enquo0(expr))
	function() {
		rep(func(), 2)
	}
}

---

Other changes

• Allow shinyDeprected() to know of superseded functions
• Document
  • Add superseded badge to renderDataTable()
  • Add superseded badge to exprToFunction(), installExprFunction()

Remaining:

• Document TODO deprecated() parameters
• Document upgrade/migration path for shinyRenderWidget
• Document quoToFunction() & handleEnvAndQuoted()
  • Explain why we're moving to quosures. One reason is that we don't have to reach to different levels using substitute. Once you have a quosure, it can be passed around safely. Normal NSE expressions are like bombs; quosures are safe to pass around.

[wch]

We can update the docs in a follow-up PR.