Fix swapped larger/smaller entries in Map.FontSizes

[jhaygood86]

Problem

Map.FontSizes has the two relative keywords crossed:

{Keywords.Larger, FontSize.Smaller},
{Keywords.Smaller, FontSize.Larger}

ValueExtensions.ToLength resolves FontSize.Larger to 120% and FontSize.Smaller to 80%, so larger resolves to the shrink factor and smaller to the grow factor — the opposite of CSS 2.1 §15.7 / CSS Fonts 3 §3.5.

Scope

The defect is latent today. DictionaryValueConverter looks the identifier up with TryGetValue(identifier, out _) and keeps only the key, discarding the mapped FontSize entirely, and Map.FontSizes has no other consumer. So nothing currently reads these values — but the table is wrong, and it becomes live the moment anything does.

Because of that, the fix is not observable through the property API. The tests therefore assert the mapping directly (the test assembly already has InternalsVisibleTo), which is what actually pins the intent:

Assert.Equal(FontSize.Larger, Map.FontSizes["larger"]);

var length = Map.FontSizes["larger"].ToLength();
Assert.Equal(Length.Unit.Percent, length.Type);
Assert.Equal(120f, length.Value);

Plus two round-trip tests confirming both keywords still parse as font-size values, so the table change doesn't disturb the converter path.

2 of the 4 fail on master. The full suite (1263 existing tests) stays green, and all seven target frameworks build with no new warnings.