Build labelDiffs cache once per update (#3211)
Build labelDiffs cache once per update (#3211)

Previously buildLabelDiffs() was called at the end of buildTicks() and
hence labelDiffs cache was calculated twice (in getMinimumBoxSize() and
then in fitBox()).

potatopeelings/Chart.js,Magnetic/Chart.js,ritesrnjn/charts,chartjs/Chart.js,chartjs/Chart.js,avlcodemonkey/Chart.js,bokysan/Chart.js,simonbrunel/Chart.js,touletan/Chart.js,rvaidya/Chart.js,simonbrunel/Chart.js,potatopeelings/Chart.js,el-ee/Chart.js,supernovel/Chart.js,touletan/Chart.js,Magnetic/Chart.js,salzhrani/Chart.js,jtcorbett/Chart.js,el-ee/Chart.js,ldwformat/Chart.js,touletan/Chart.js,salzhrani/Chart.js,touletan/Chart.js,ldwformat/Chart.js,2Ring/Chart.js,avlcodemonkey/Chart.js,nicktiberi/Chart.js,2Ring/Chart.js,nicktiberi/Chart.js,bokysan/Chart.js,panzarino/Chart.js,chartjs/Chart.js,panzarino/Chart.js,chartjs/Chart.js,jtcorbett/Chart.js,nnnick/Chart.js,amir-hadzic/Chart.js,amir-hadzic/Chart.js,supernovel/Chart.js,ritesrnjn/charts,rvaidya/Chart.js