`MultiBuffer::anchor_in_excerpt` currently just wraps the given text anchor in a multibuffer anchor. This allows one to get a multibuffer anchor that points outside its excerpt which is basically never what one wants. This PR now does a bounds check and returns `None` if the given text anchor is not within the bounds of the excerpt. Release Notes: - N/A *or* Added/Fixed/Improved ... Co-authored-by: Kirill Bulatov <kirill@zed.dev>