DataBar().LowestValue()/HighestValue() emitted the x14 extension cfvo nodes as type="num" with a formula of 0 instead of type="min"/"max". Strict readers such as WPS Spreadsheets honor that value and lock the bar thresholds to 0, so the data bar renders incorrectly.
The extension converter unconditionally overwrote the cfvo type with Numeric whenever a threshold value was present. LowestValue()/HighestValue() store a placeholder "0", so their automatic min/max bounds were turned into fixed numeric thresholds; the same override also collapsed percent, percentile and formula thresholds to num.
Each cfvo is now built from its content type: automatic bounds stay autoMin/autoMax, lowest/highest bounds become min/max with no formula, and value based thresholds keep their type and emit the formula.
Fixes#2843