Show renderDataTable deprecation message by default

[hedsnz]

Related to #3627.

• shiny::renderDataTable has been deprecated since shiny 0.11.1, but the deprecation warning was only shown in dev mode.
• This PR turns on that deprecation message by default.
• Increasing visibility of this change is the first step toward eventually hard-deprecating shiny::renderDataTable and shiny::dataTableOutput in favour of the DT equivalents, allowing shiny to remove its dependency on DataTables.

[jonthegeek]

The description of "Superseded" might make this difficult (see #3627 (comment) ).

[jcheng5]

Hmmm, I used the GitHub button to rebase the branch against main and now CI is failing.

Edit: Fixed, the problem was with the GHA workflow, nothing to do with this PR.

[hedsnz]

@jcheng5 Any update on this, and/or #3627 in general?

[raulbla]

Is this PR still ongoing?

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