Please add a "remove leading and trailing whitespace setting" when copying a single line of text

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promoted from MSFT:43799361

> Frequently I use "git branch" to list out branches, and then triple click on one of them to highlight it, and then right-click to copy it. I then do "git checkout" followed by Ctrl+V to checkout this branch.
>
> When I do this, there's always whitespace at the front of the branch name that was copied.
>
> This is just one concrete example, but this happens all the time. When copying a single line of text it is very rare that the user is trying top copy the entire line of output as-is.
>
> Can you please add a setting that removes leading whitespace when copying. It should apply only to single-line copies.

We could probably add a `"trimWhitespace": "none" | "trailing" | "leading" | "all"` param to `copy`. That seems kinda sensible. The equal of the `paste` property.

Start by tracing the terminal's copy entry point and comparing it with the existing paste property. Define how the proposed trimWhitespace options apply only to single-line copies, then verify the behavior for none, trailing, leading, and all whitespace modes.

Written by the indexing model from the issue text.