Random-effects sig contours

[BalancedmonkeY]

Currently the extended funnel plot can only add significance contours/regions for fixed-effects meta-analyses. Need to include random-effects. This cannot be done with a closed-form expression, so previous code split the space into small squares and then coded accordingly. I found that geom_tile() may be helpful to replicate - but struggled to design an efficient piece of code to do this.