This completely reworks URL highlighting to fix two issues which were
caused by the original approach.
The primary issues that were not straight-forward to resolve with the
previous implementation were about handling the URL highlighted content
moving while the highlight is active.
This lead to issues with highlighting with scrolling and when the
display offset was not 0.
The new approach sticks closely to prior art done for the selection,
where the selection is tracked on the grid and updated whenever the
buffer is rotated.
The truncation of URLs was incorrectly assuming input to be just a
single codepoint wide to truncate the end of URLs with unmatching
closing parenthesis. This is now handled properly using Rust's built-in
Unicode support.
This fixes#2231.
This fixes#2225.
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