[api-minor] Convert getJSActions to return data in a Map

[Snuffleupagus]

Compared to regular Objects there's a number of advantages to using Maps:

• They support proper iteration.
• They have a simple way to check for the existence of data.
• They have a simple/efficient way to check the number of elements.

If this functionality was added today, I cannot imagine that we'd choose an Object for this data.

Note also how in the scripting-implementation the actions were already converted into a Map, via the createActionsMap helper.
In the Firefox PDF Viewer sending Maps to the scripting-implementation should be fine, since it uses the browser Cu.cloneInto functionality; see https://searchfox.org/firefox-main/source/toolkit/components/pdfjs/content/PdfSandbox.sys.mjs
However with QuickJS, used by the GENERIC viewer, all data needs to be stringified and unfortunately JSON.stringify() doesn't support Maps. Hence we convert Maps to Objects, via a replacer function, since the existing createActionsMap usage will convert the actions-Objects back to Maps.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.96%. Comparing base (73707b6) to head (803c9d7).

Files with missing lines	Patch %	Lines
src/display/annotation_layer.js	90.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21664   +/-   ##
=======================================
  Coverage   89.96%   89.96%           
=======================================
  Files         263      263           
  Lines       66886    66890    +4     
=======================================
+ Hits        60171    60179    +8     
+ Misses       6715     6711    -4     

Flag	Coverage Δ
browsertest	66.54% <52.00%> (+0.01%)	⬆️
fonttest	9.04% <0.00%> (ø)
integrationtest	69.34% <96.42%> (+0.01%)	⬆️
unittest	57.57% <50.00%> (+<0.01%)	⬆️
unittestcli	56.51% <44.00%> (-0.01%)	⬇️

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[Snuffleupagus]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Linux m4)

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Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.241.84.105:8877/50b1eccdace79dc/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

---

Received

Command cmd_browsertest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.193.163.58:8877/6b92c54280df5bc/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/50b1eccdace79dc/output.txt

Total script time: 18.24 mins

• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

---

Success

Full output at http://54.193.163.58:8877/6b92c54280df5bc/output.txt

Total script time: 24.07 mins

• Regression tests: Passed

[timvandermeij]

Looks good; thank you!