Fix LeakyReLU image (#78508)
Fixes #56363, Fixes #78243
| [Before](https://pytorch.org/docs/stable/generated/torch.nn.LeakyReLU.html) | [After](https://docs-preview.pytorch.org/78508/generated/torch.nn.LeakyReLU.html) |
| --- | --- |
|  |  |
- Plot `LeakyReLU` with `negative_slope=0.1` instead of `negative_slope=0.01`
- Changed the title from `"{function_name} activation function"` to the name returned by `_get_name()` (with parameter info). The full list is attached at the end.
- Modernized the script and ran black on `docs/source/scripts/build_activation_images.py`. Apologies for the ugly diff.
```
ELU(alpha=1.0)
Hardshrink(0.5)
Hardtanh(min_val=-1.0, max_val=1.0)
Hardsigmoid()
Hardswish()
LeakyReLU(negative_slope=0.1)
LogSigmoid()
PReLU(num_parameters=1)
ReLU()
ReLU6()
RReLU(lower=0.125, upper=0.3333333333333333)
SELU()
SiLU()
Mish()
CELU(alpha=1.0)
GELU(approximate=none)
Sigmoid()
Softplus(beta=1, threshold=20)
Softshrink(0.5)
Softsign()
Tanh()
Tanhshrink()
```
cc @brianjo @mruberry @svekars @holly1238
Pull Request resolved: https://github.com/pytorch/pytorch/pull/78508
Approved by: https://github.com/jbschlosser
