When text_overflow (e.g. text_ellipsis) was combined with line_clamp > 1,
the previous approach computed a flat width budget (wrap_width * max_lines)
and truncated the text as a single line. When the truncated text was then
word-wrapped, waste at line-break boundaries could push extra content onto
the last line, causing it to overflow and get clipped without a visible
ellipsis.

Add LineWrapper::truncate_wrapped_line(), which walks through characters
in a single pass tracking both wrap boundaries and the truncation point
simultaneously. On the last allowed line, it truncates and appends the
affix (e.g. "…") so the result fits within wrap_width when re-wrapped.

Newlines are handled as forced line breaks that consume one of the
max_lines budget. A newline encountered on the last allowed line triggers
truncation with the affix, since more content follows below.

For max_lines == 1 or TruncateFrom::Start, it delegates to the existing
truncate_line() with the flat budget, preserving current behavior.