Use custom dispatcher for Function.prototype routines (#2967)

Binary size gain:
     - Intel: ~70B (gcc-7.3)
     - Arm: 50 B (arm-linux-gnueabi-gcc-7.3)

Co-authored-by: Gabor Loki loki@inf.u-szeged.hu
JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

Author: rerobika