Add support for shiny.autoreload

[kamilzyla]

Changes

Supersedes PR #528, addresses issues #339, #552. Add support for automatic reloading with options(shiny.autoreload = TRUE).

How to test

Set options(shiny.autoreload = TRUE) and run a Rhino app. Modify e.g. main.R - the app should automatically reload and show the changes. It should work with all settings of legacy_entrypoint with the exclusion of app_dir.

[codecov-commenter]

Codecov Report

Attention: 29 lines in your changes are missing coverage. Please review.

Comparison is base (84bc815) 29.31% compared to head (6d7a914) 28.57%.

❗ Current head 6d7a914 differs from pull request most recent head 976b8b9. Consider uploading reports for the commit 976b8b9 to get more accurate results

Files	Patch %	Lines
R/app.R	14.70%	29 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #559      +/-   ##
==========================================
- Coverage   29.31%   28.57%   -0.75%     
==========================================
  Files          10       10              
  Lines         481      511      +30     
==========================================
+ Hits          141      146       +5     
- Misses        340      365      +25     

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[jakubnowicki]

Works fine, but I would love to hear the opinion from @TymekDev , as he did more research on autoreloading.

[TymekDev]

Looks good! Clean changes and well documented.

I was about to suggest a mention about shiny::devmode for enabling autoreload, but I see it is marked as an experimental (for a couple of years now), so it's up to you if you include it in the vignette.