Issue Summary

This is reproducible on Data Center: N/A

Steps to Reproduce

1. Go to PR with code diff
2. Highlight a few lines of code and copy to clipboard 
3. Click "Add comment" button to open comment editor 
4. Paste content from clipboard into the blank editor (by default it uses paragraph formatting)
5. For example, if you copied this diff to your clipboard:

Expected Results

Pasted content only includes code 

Actual Results

Pasted content includes code, line numbers, extra lines, "Added" or "Removed" text

function sayHey(name?: string): string {

2
+Added:  return `Hey ${name}!`;

3
+Added:} 

Workaround

User can paste content into a code block (by clicking code block option from editor or using 3 back ticks) and it will be formatted correctly.