fix/perf(is): improve perf of isPlainObject and avoid problems with Symbol.toStringTag (#12715)
fix/perf(is): improve perf of isPlainObject and avoid problems with Symbol.toStringTag (#12715)

- see https://github.com/quasarframework/quasar/commit/f4c84adca0138eb6dba64c9a7977c4363b07f6f1#commitcomment-68102067
quasarframework/quasar,quasarframework/quasar,rstoenescu/quasar-framework,quasarframework/quasar,quasarframework/quasar,rstoenescu/quasar-framework,rstoenescu/quasar-framework