text that glyph_item corresponds to (glyph_item->item->offset is an offset from the start of text)
an array whose length is the number of characters in glyph_item (equal to glyph_item->item->num_chars) to be filled in with the resulting character widths.
Given a PangoGlyphItem and the corresponding text, determine the screen width corresponding to each character. When multiple characters compose a single cluster, the width of the entire cluster is divided equally among the characters. See also pango_glyph_string_get_logical_widths(). Since 1.26