Convert a spicy flextable output to a plain flextable
Source:R/regression_dispatch.R
as_flextable.spicy_flextable.Rdtable_regression() and table_continuous_lm() return their
output = "flextable" tables with a lightweight spicy_flextable
class tag whose only job is HTML note styling. Every flextable
verb already works on the tagged object; this method returns the
clean underlying flextable::flextable() – the note is already
part of its footer – for workflows that want the untagged object
(e.g. custom knit hooks, flextable::save_as_docx() pipelines, or
composition with other flextable tooling), mirroring
gtsummary::as_flex_table().