Move DECRQSS response encoding into the terminal DCS handler so both
the full termio path and libghostty-vt terminal stream emit the same
replies. The C API stream now maintains and releases DCS parser state
and forwards responses through write_pty.
XTGETTCAP queries are a semicolon-delimited list of hex encoded terminfo
capability names. Ghostty encodes a map using upper case hex encodings,
meaning when an application uses a lower case encoding the capability is
not found. To fix, we convert the entire list we receive in the query to
upper case prior to processing further.
Fixes: #7229
Only SGR, DECSCUSR, DECSTBM, and DECSLRM are handled, as these are the
only ones that Ghostty supports (as far as I can tell) and are the only
ones that seem actually useful.
