Function zng_wgt_text::get_lines_len

pub fn get_lines_len(
    child: impl UiNode,
    len: impl IntoVar<usize>,
) -> impl UiNode

P Gets the number of lines in the text, including wrap lines.

This is very cheap, the text widget already has the length, but it does include wrapped lines. You can use get_lines_wrap_count to get text lines and a count of wrapped lines for each.