I left the getLineHieght and other getters in BitmapFont since they are convenient and are used a lot. It doesn't make sense to have setters (like setScale) in BitmapFont though. Modification of the BitmapFontData should be done through BitmapFontData, else it makes it seem like the setting is per BitmapFont.
Use GlyphLayout! Also, often BitmapFont#getBounds was just used for alignment. In that case, use the BitmapFont#draw methods that allow alignment to be specified.