feat: add +/- notation option to Diff operation

[Sushanth012]

Closes #2312

Added a "Show +/- notation" boolean option to the Diff operation (default: false).

When enabled:

• Added lines are prefixed with "+ "
• Removed lines are prefixed with "- "
• Unchanged lines are prefixed with " " (two spaces)

Output is compatible with standard unified diff format, allowing export to tools like Slack's diff snippet viewer. Existing highlighting behavior is unchanged when the option is off.

[CLAassistant]

All committers have signed the CLA.

[C85297]

Hi @Sushanth012 , thank you for the pull request!

I am worried the changes might not have the effect you desire in certain conditions - such as if diffChars is selected. Your code assumes that the returned value from jsdiff is split by lines, but I don't believe this to always be the case.

Could you confirm if you've tested this locally, and ideally provide screenshots so we can review the UI behaviour?
And could you also add a test case (unfortunately there isn't an existing one for Diff, but you could copy one of the tests in tests/operations/tests and implement a test just for this +/- functionality)

[C85297]

@Sushanth012 jsdiff does seem to support a patch mode, might that solve your problem?