在平面直角坐标系中,对于点$M\left(x,y\right)$和$N\left(x,{y\’}\right)$给出如下定义:如果${y\’}=\left\{\begin{array}{l}y(x≥0)\\-y(x＜0)\end{array}\right.$,那么称点$N$为点$M$的"关联点".例如:点$\left(4,2\right)$的"关联点"为点$\left(4,2\right)$,点$\left(-4,2\right)$的"关联点"为点$\left(-4,-2\right)$.
$(1)$点$\left(6,-6\right)$的"关联点"为$\left(m,n\right)$,则$m+n=\_\_\_\_\_\_.$
$(2)$如果点${P\’}\left(a,3\right)$是一次函数$y=x-2$图象上点$P$的"关联点",那么点$P$的坐标为______.