Make drag shadow grapheme cluster aware.

[start, min(end, DRAG_SHADOW_MAX_TEXT_LENGTH)) was used to make drag
shadow. It ignores grapheme cluster, so unexpected shadow was created for
characters that contain multiple code units.

Bug: 23097276
Change-Id: Ic7d34ec02ea04a3f17337e4253babac87ef3b03c
1 file changed