fix: refine cursor positioning using pixel-based calculations

[mkslanc]

Issue #, if available:

Description of changes:

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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

Open kitchen-sink @ dc57d2d5a823c447836621c9286862790aea6d31

Open kitchen-sink @ f8231bc63aa6239bb0768857f1fa38c929908337

Open kitchen-sink @ 2ac3f77c83b2e874497182793f85358fa3624819

Open kitchen-sink @ 02c76f982a9c569a65538885ebbac8377a6e6e17

[nightwing]

This does not work when editor position on screen changes (try collapsing sidebar), and does not work on multiselect, since each selection has it's own selection object.
I think there is no need to introduce desiredPixelPos, instead of that we should update desired column the way we do when rendering markers, and save as column, (that would keep correct position even when font size changes).

Also updateSelectionPixelConversion method is pretty bad, we need only to add fontmetrics to selection, we should not dynamically add methods to classes.

It is also possible to add fontmetrics directly to session, that way tmpsel at https://github.com/ajaxorg/ace/blob/master/src/multi_select.js#L504 will get correct fontmetrics automatically.