fix(fullscreen): (backport from Qv2) keep count of fullscreen elements (#11624)
fix(fullscreen): (backport from Qv2) keep count of fullscreen elements (#11624)

* fix(fullscreen mixin): keep count of fullscreen elements

* Update fullscreen.js

Co-authored-by: Razvan Stoenescu <5ced39d27860b435bebb748c5dedb4e40f3b0e82@gmail.com>
pdanpdan/quasar,pdanpdan/quasar,pdanpdan/quasar,pdanpdan/quasar