Add LeakyReLU operator to static runtime (#47798)
Summary:
- Add LeakyReLU operator to static runtime
- Add LeakyReLU benchmark
- Add LeakyReLU correctness test case
Static Runtime
```
------------------------------------------------------------------------------
Benchmark Time CPU Iterations
------------------------------------------------------------------------------
BM_leaky_relu/1 4092 ns 4092 ns 172331
BM_leaky_relu/8 4425 ns 4425 ns 158434
BM_leaky_relu/20 4830 ns 4830 ns 145335
BM_leaky_relu_const/1 3545 ns 3545 ns 198054
BM_leaky_relu_const/8 3825 ns 3825 ns 183074
BM_leaky_relu_const/20 4222 ns 4222 ns 165999
```
Interpreter
```
------------------------------------------------------------------------------
Benchmark Time CPU Iterations
------------------------------------------------------------------------------
BM_leaky_relu/1 7183 ns 7182 ns 96377
BM_leaky_relu/8 7580 ns 7580 ns 91588
BM_leaky_relu/20 8066 ns 8066 ns 87183
BM_leaky_relu_const/1 6466 ns 6466 ns 107925
BM_leaky_relu_const/8 7063 ns 7063 ns 98768
BM_leaky_relu_const/20 7380 ns 7380 ns 94564
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47798
Reviewed By: ezyang
Differential Revision: D24927043
Pulled By: kavoor
fbshipit-source-id: 69b12cc57f725f1dc8d68635788813710a74dc2b
