fix(module:code-editor): memorize cursor position and selections

[Airblader]

Calling #setValue() on a monaco editor instance causes the mouse cursor to jump to the
beginning of the document, which is undesirable for a ControlValueAccessor implementation
which should only update the content. Also see
microsoft/monaco-editor#1397 for more information.

Unfortunately, using #executeEdits() doesn't really work as a replacement because it will
mess with selections. Therefore we memorize and restore the cursor position before/after
setting the value. Since #setValue() also causes a selection to be lost we do the same for
those. Restoring selections may produce slightly unexpected results if the selection covers
part of the content that has been changed, but is still preferable to losing the selection
altogether.

fixes #6038

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features) (there are no working code-editor tests)
• Docs have been added / updated (for bug fixes / features) (not required)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[Airblader]

CC @sorahn

[codecov]

Codecov Report

Merging #6044 (9a1ec8c) into master (679be27) will decrease coverage by 0.04%.
The diff coverage is 18.75%.

@@            Coverage Diff             @@
##           master    #6044      +/-   ##
==========================================
- Coverage   89.95%   89.90%   -0.05%     
==========================================
  Files         465      465              
  Lines       14042    14055      +13     
  Branches     2307     2310       +3     
==========================================
+ Hits        12631    12636       +5     
- Misses        863      872       +9     
+ Partials      548      547       -1     

Impacted Files	Coverage Δ
components/code-editor/code-editor.component.ts	14.78% <18.75%> (+1.05%)	⬆️
components/core/util/text-measure.ts	91.30% <0.00%> (+1.73%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 679be27...9a1ec8c. Read the comment docs.