Misc. small optimizations in Grappler and shape inference code.

Impact on time per optimizer on inception graph:

model_pruner:          590 ms -> 550 ms   (-7%)
function_optimizer:    130 ms -> 130 ms   (-0%)
constant_folding:     7600 ms -> 7550 ms  (-0.7%)
arithmetic_optimizer: 1860 ms -> 1550 ms  (-20%)
loop_optimizer:        320 ms -> 320 ms   (-0%)
dependency_optimizer: 1300 ms -> 720 ms   (-45%)
layout:               1400 ms -> 1400 ms  (-0%)
memory_optimizer:     4200 ms -> 3540 ms  (-16%)
PiperOrigin-RevId: 192694528