000a1916

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Add OscSequence token to parse and discard OSC escape sequences

GHC emits OSC 8 hyperlink sequences in warning messages (e.g. for
error code documentation URLs). These begin with ESC ] and end with
the String Terminator (ESC \) or BEL. The tokenizer previously only
handled CSI sequences (ESC [), so OSC bytes leaked through as plain
text.

Add OscSequence to AnsiToken, oscSequenceP to the tokenizer, and
handle it as a discard in tokensToChunks. Update stripAnsi in the
test helper to also strip OSC sequences so the concatenation property
test remains valid.