Micro-optimizations for qsFullScreen

Note that setScrollingEnabled needs to be called when the state is
updated regardless of whether qsFullScreen changes or not, so I moved
it back to where it was prior to ag/26643429.

Bug: 331878115
Test: https://dashboards.corp.google.com/view/_253ba238_3acf_45bf_981e_4fcbab46ca26?p=INVOCATIONS:I06000010266669753,I51500010266100726,I90700010267636750,I52500010268172561,I89000010268113396,I82500010276381802&p=INVOCATION_NAMES:good,bad,flag_off,qsFullScreen,shadeExpansion,optimized&f=class_name:in:OpenScrollNotificationShadeMicrobenchmark&av=sskz5j:kwkjon
Flag: EXEMPT trivial change

Change-Id: I6112ca062cda2239a04481ebcd1442b713453cae