fix: Fix typeerror in font metrics getZoom

[akoreman]

Issue #, if available: NA

Description of changes: The type check in the build started failing recently:

likely due to a new typescript version being used by the Github action. This change explicitly constructs a Number from
window.getComputedStyle(element)["zoom"] to prevent these type issues.

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 86.79%. Comparing base (16c95b3) to head (1a1e9fd).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5600   +/-   ##
=======================================
  Coverage   86.79%   86.79%           
=======================================
  Files         594      594           
  Lines       43091    43091           
  Branches     7147     7147           
=======================================
  Hits        37400    37400           
  Misses       5691     5691           

Flag	Coverage Δ
unittests	86.79% <100.00%> (ø)

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