chore: small tweaks LineWidget type

[akoreman]

Issue #, if available: NA

Description of changes: In #5673, we recently exposed LineWidget interface, this makes some small tweaks to it by making hidden, editor and session optional bringing the external type definition a bit closer to the internal type.

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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

[github-actions]

One of the public type files has been updated, plase make sure there are no backwards incompatible changes done in the PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.01%. Comparing base (442680c) to head (da3496e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5683   +/-   ##
=======================================
  Coverage   87.01%   87.01%           
=======================================
  Files         598      598           
  Lines       43683    43683           
  Branches     7204     7204           
=======================================
  Hits        38012    38012           
  Misses       5671     5671           

Flag	Coverage Δ
unittests	87.01% <ø> (ø)

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