Fix #2797 - outputinvalidated events missed for outputs not in DOM

[earlygrey]

This is a PR for the issue identified in https://github.com/rstudio/shiny/issues/2797.

The PR contains 3 commits - the first contains the changes to the source js files, the second adds the built js files, the third adds the description to NEWS.md.

I think the code is self explanatory and I describe it a little in the issue. It creates an array called $invalidateOutputQueue, which flags shiny:outputinvalidated events corresponding to html elements not in the DOM (eg in a closed modal). It triggers the event if the output is later added (eg the modal opened) and if the flag has not already been cleared (by shiny:value or shiny:unbound events).

I've run test-all.R:

> test_check("shiny")
══ testthat results  ═══════════════════════════════════════
[ OK: 1055 | SKIPPED: 6 | WARNINGS: 0 | FAILED: 0 ]

Please let me know if there's anything I've missed which I should have done, or anything I've done incorrectly.

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[cpsievert]

Thanks for this impressive PR @earlygrey! Turns out, there's a few different scenarios in which .recalculating class doesn't get properly properly attached to recalculating output. #4039 aims to fix those scenarios, including #2797, so I'll be closing this.