fix: fixed the issue of Copying entire code snippet on text selection

[nawinsharma]

PR Fixes the issue of Copying entire code snippet on text selection,

now,Only the selected portion of the code snippet is highlighted.

Resolves #1764

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] I assure there is no similar/duplicate pull request regarding same issue

[nawinsharma]

@devsargam, can you review it once..