Fixes b/15734816 In the text "Wi-Fi", "-Fi" appears bolder than "Wi"
The problem was caused by "stickiness" in choosing fonts, where layout
would prefer using a font used for preceding characters as long as it
mapped the following characters in a run, in favor of the "best match"
rules. This patch adds a whitelist for making the stickiness more
conservative, only applying it for characters necessary for correct
shaping (ZWJ and ZWNJ in particular) and basic punctuation, where it is
desirable to match the style of the preceding text.
Change-Id: I1cf116879f074a5a71c351846707bfdd07b0d320
ba5dbb6f24