(closes #1010, #1910, #719, #798, #1648) Generate PSy-layers and Kernel Subs using PSyIR lowering (instead of gen_code/f2pygen)

(closes #1010, #1910, #719, #798, #1648) Generate PSy-layers and Kernel Subs using PSyIR lowering (instead of gen_code/f2pygen) #1347