lib/fonts: Refactor glyph-rotation helpers

lib/fonts: Refactor glyph-rotation helpers

Change the signatures of the glyph-rotation helpers to match their
public interfaces. Drop the inline qualifier.

Rename several variables to better match their meaning. Especially
rename variables to bit_pitch (or a variant thereof) if they store
a pitch value in bits per scanline. The original code is fairly
confusing about this. Move the calculation of the bit pitch into the
new helper font_glyph_bit_pitch().

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>