Fix autocomplete popup positioning with CSS transforms

[cyphercodes]

Issue #, if available:
Fixes #5688

Description of changes:

• Position the autocomplete popup using the renderer's CSS-transform coordinate mapper when hasCssTransforms is enabled.
• Use the transformed line height/ghost-text offset for popup placement decisions so scaled editors anchor the popup next to the transformed cursor.
• Add regression coverage for transformed popup coordinates.

Verification:

• npm test -- --grep "popup positioning accounts for editor css transforms"
• npx mocha ./src/autocomplete_test.js ./src/autocomplete/popup_test.js --exit --color
• npx eslint src/autocomplete.js src/autocomplete_test.js
• git diff --check HEAD~1..HEAD

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Pull Request Checklist:

• No backwards incompatible changes were made to Ace's public interface which is defined through the main typings file (ace.d.ts) and its references:
  • https://github.com/ajaxorg/ace/blob/master/ace.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-modes.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-extensions.d.ts

Open kitchen-sink @ 2cc6417e777f1e7a4666da6c86ed13d70a9aa673

Open kitchen-sink @ b399e9431752a2d4a63eceb2c0922df624582077

[codecov]

Codecov Report

❌ Patch coverage is 94.04762% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.70%. Comparing base (f82010e) to head (2cc6417).

Files with missing lines	Patch %	Lines
src/autocomplete.js	88.46%	3 Missing ⚠️
src/autocomplete_test.js	96.55%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5984      +/-   ##
==========================================
- Coverage   93.73%   93.70%   -0.03%     
==========================================
  Files         641      641              
  Lines      138167   138245      +78     
  Branches    14561    14552       -9     
==========================================
+ Hits       129510   129546      +36     
- Misses       8657     8699      +42     

Flag	Coverage Δ
unittests	93.70% <94.04%> (-0.03%)	⬇️

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[cyphercodes]

Added focused coverage for the transformed ghost-text popup positioning path that Codecov flagged.

Verification:

• npx mocha ./src/autocomplete_test.js --exit -p --color
• git diff --check