Drop "virtualized" from TERMINAL_CHART_HOLDER_STATES so an off-screen holder
that never mounted or painted is not counted as a ready/terminal state.
#42901 grows the standalone-capture viewport so off-screen holders mount, but a
holder still virtualized at readiness time -- e.g. a dashboard taller than the
capture viewport cap -- was previously counted terminal and could ship a blank
region. Treating it as not-ready makes the readiness gate fail loud (via the
webdriver unready check) and drops semantic_success rather than silently
delivering a partially blank capture.
virtualized_holders is still reported directly from the state counts, so the
diagnostic logging is unchanged; only ready/unready/semantic_success shift.