Some Default_Ignorable_Code_Points are not given zero width

[Jules-Bertholet]

From https://www.unicode.org/faq/unsup_char.html#3:

All default-ignorable characters should be rendered as completely invisible (and non advancing, i.e. “zero width”), if not explicitly supported in rendering.

However, this library does not assign a zero width to all such characters; notably U+3164 HANGUL FILLER and U+FFA0 HALFWIDTH HANGUL FILLER are incorrectly assigned nonzero width. (There is one exception where this library is correct in assigning a nonzero width to a Default_Ignorable_Code_Point: U+115F HANGUL CHOSEONG FILLER has no display on its own, but it combines with medial and trailing Hangul jamo (which are assigned width 0) to form a width-2 Hangul syllable block, and therefore width 2 is correct for it.)