Cache the result of buildSymbolGlyphIdEncoding (PR 21726 follow-up)

[Snuffleupagus]

If a PDF document contains multiple (different) non-embedded /Identity encoded Symbol fonts, or once cleanup has been triggered by the viewer, the "SymbolGlyphIdEncoding" would need to be recomputed more than once.
By updating the getLookupTableFactory helper to be able to create an Array, and not just an Object, it's easy enough to both lazily initialize and cache the "SymbolGlyphIdEncoding" (similar to e.g. the existing glyph-maps).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.10%. Comparing base (c2bbde1) to head (389ddde).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21740   +/-   ##
=======================================
  Coverage   90.09%   90.10%           
=======================================
  Files         264      264           
  Lines       67194    67233   +39     
=======================================
+ Hits        60538    60578   +40     
+ Misses       6656     6655    -1     

Flag	Coverage Δ
browsertest	66.35% <100.00%> (-0.04%)	⬇️
fonttest	9.00% <66.66%> (+<0.01%)	⬆️
integrationtest	69.30% <66.66%> (+0.02%)	⬆️
unittest	58.22% <66.66%> (-0.04%)	⬇️
unittestcli	56.60% <66.66%> (-0.04%)	⬇️

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[Snuffleupagus]

/botio browsertest

[moz-tools-bot]

From: Bot.io (Windows)

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Received

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

Live output at: http://54.193.163.58:8877/0ed17f52614bedd/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

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

Live output at: http://54.241.84.105:8877/80444e1e8c0cd5d/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/80444e1e8c0cd5d/output.txt

Total script time: 16.79 mins

• Regression tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

---

Success

Full output at http://54.193.163.58:8877/0ed17f52614bedd/output.txt

Total script time: 23.83 mins

• Regression tests: Passed

[timvandermeij]

Looks good; thank you for improving this!