fix: ghost text rendering of empty lines

[akoreman]

Issue #, if available: NA

Description of changes: In the ghost text, we set the content of a line as the text content of a div. For lines without any text (e.g. when the suggestion has a line of white space) this results in a div without any contents, which most browsers will not render. This change sets a space as the text content if it's empty to ensure the empty lines get rendered.

Before this change:

Screen.Recording.2024-07-18.at.11.30.30.mov

After:

Screen.Recording.2024-07-18.at.11.29.58.mov

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.89%. Comparing base (ed233cf) to head (b60cd72).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5615   +/-   ##
=======================================
  Coverage   86.89%   86.89%           
=======================================
  Files         594      594           
  Lines       43143    43151    +8     
  Branches     7150     7151    +1     
=======================================
+ Hits        37489    37497    +8     
  Misses       5654     5654           

Flag	Coverage Δ
unittests	86.89% <100.00%> (+<0.01%)	⬆️

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