fix: apply padding to right side multi-line markers

[akoreman]

Issue #, if available: NA

Description of changes: Currently, we apply a padding of 4px to the left side of multi line markers but no padding to the right side, making it hard to style both edges the same way. This adds a 4px padding to the right side of multi line selections.

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Pull Request Checklist:

• [x] 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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.97%. Comparing base (a6ead2f) to head (2b7a830). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5636 +/- ## ======================================= Coverage 86.97% 86.97% ======================================= Files 594 594 Lines 43395 43395 Branches 7170 7170 ======================================= Hits 37742 37742 Misses 5653 5653 ``` | [Flag](https://app.codecov.io/gh/ajaxorg/ace/pull/5636/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ajaxorg) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/ajaxorg/ace/pull/5636/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ajaxorg) | `86.97% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ajaxorg#carryforward-flags-in-the-pull-request-comment) to find out more.

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