[mlir] Add polynomial approximation for math::ExpM1

This approximation matches the one in Eigen.

```
name                      old cpu/op  new cpu/op  delta
BM_mlir_Expm1_f32/10      90.9ns ± 4%  52.2ns ± 4%  -42.60%    (p=0.000 n=74+87)
BM_mlir_Expm1_f32/100      837ns ± 3%   231ns ± 4%  -72.43%    (p=0.000 n=79+69)
BM_mlir_Expm1_f32/1k      8.43µs ± 3%  1.58µs ± 5%  -81.30%    (p=0.000 n=77+83)
BM_mlir_Expm1_f32/10k     83.8µs ± 3%  15.4µs ± 5%  -81.65%    (p=0.000 n=83+69)
BM_eigen_s_Expm1_f32/10   68.8ns ±17%  72.5ns ±14%   +5.40%  (p=0.000 n=118+115)
BM_eigen_s_Expm1_f32/100   694ns ±11%   717ns ± 2%   +3.34%   (p=0.000 n=120+75)
BM_eigen_s_Expm1_f32/1k   7.69µs ± 2%  7.97µs ±11%   +3.56%   (p=0.000 n=95+117)
BM_eigen_s_Expm1_f32/10k  88.0µs ± 1%  89.3µs ± 6%   +1.45%   (p=0.000 n=74+106)
BM_eigen_v_Expm1_f32/10   44.3ns ± 6%  45.0ns ± 8%   +1.45%   (p=0.018 n=81+111)
BM_eigen_v_Expm1_f32/100   351ns ± 1%   360ns ± 9%   +2.58%    (p=0.000 n=73+99)
BM_eigen_v_Expm1_f32/1k   3.31µs ± 1%  3.42µs ± 9%   +3.37%   (p=0.000 n=71+100)
BM_eigen_v_Expm1_f32/10k  33.7µs ± 8%  34.1µs ± 9%   +1.04%    (p=0.007 n=99+98)
```

Reviewed By: ezhulenev

Differential Revision: https://reviews.llvm.org/D101852