Highlighter options (straighten the line)

## Use case

It's not working when the box is checked. I'm highlighting text, and I have to work hard to make the highlight as straight as possible. It's frustrating. I've tried pressing shift and ctrl (maybe I was missing something), but those don't help make the lines straight. What does "Straighten the line" actually mean then?

## Suggested solution

When clicking to highlight the text, show a guideline of what will actually be highlighted, a preview of the highlighted text you'll see. The output should be a straight highlight across the text.

If you want to have freehand as the default, perhaps letting the user press "space bar" (or whatever assigned key) while clicking to highlight the text to trigger the straighten the line feature.

### Possible drawbacks

I'm new to this, so I'm hoping it's user error. Please tell me how to make the highlight straight.

### Possible alternatives

No files, tests, or implementation entry points are named. Reproduce the checked “Straighten the line” behavior in the Drawing app, then trace the highlighter interaction to determine whether the option should preview and produce a straight highlight; done means the behavior is clear and works consistently.

Written by the indexing model from the issue text.