ATSUI spacing features with negative values

Test for negative spacing values in complex text rendering.

Each green box should be identical to the blue box it follows, except for accents.

Word spacing	Letter spacing
יְהִי, אָחִי, לְךָ סֵפֶר שְׁלַחְתִּיו וּמִמְכֶּרֶת צְמִיתוּת לָךְ מְכַרְתִּיו. Lorèm ipsum dolor sit amèt, consectetuer adipiscing èlit. Lorem ipsum dolor sit amet, consectetuer adipiscing elit.	יְהִי, אָחִי, לְךָ סֵפֶר שְׁלַחְתִּיו וּמִמְכֶּרֶת צְמִיתוּת לָךְ מְכַרְתִּיו. Lorèm ipsum dolor sit amèt, consectetuèr adipiscing èlit. Lorem ipsum dolor sit amet, consectetuer adipiscing elit.