Fix copy-paste of code blocks with code callouts

[reakaleek]

Changes

Removes trailing spaces after a line in a code block. If there is a code callout it will add an empty span with the width of the removed spaces.

The will preserve alignment of code callouts.

Additionally, use css ::after element for the code callout index number to make sure it can't be copied.

How to test

0. Go to https://docs-v3-preview.elastic.dev/elastic/docs-builder/pull/946/syntax/code#align-callouts
1. And copy the code snippet:
   • with the copy button
   • and while selecting the text and copy it
2. The pasted code should not have any trailing white spaces

[leemthompo]

🙌 thanks!