[Bug]: add_subfigure does not respect GridSpec parameters

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### Bug summary

According the documentation for `Figure.add_subfigure`, you should be able to use `GridSpec` to create a set of subfigures to fill a certain space of a parent figure. However, no matter what settings are input into `GridSpec`, the parent figure is divided into equally sized subfigures. Doing this same process with `Figure.add_subplot` produces the expected results with the axes bounded by the input extent and separated by the correct `hspace` and `wspace`.

### Code for reproduction

```Python
import matplotlib.pyplot as plt
from matplotlib.gridspec import GridSpec
import numpy as np

dpi = 100
width = 600
height = 600

main = plt.figure(figsize=(width / dpi, height / dpi), dpi=100,
facecolor='#9a9a9a', frameon=False)

gs = GridSpec(2, 4, left=.1, right=.9, bottom=0.1,
top=0.9, wspace=0.15, hspace=0.15)

colors = np.array([
['red', 'black', 'green', 'blue'],
['brown', 'gray', 'white', 'gold']
])

panels = []
for row in range(2):
for col in range(4):
main.add_subfigure(gs[row, col], facecolor=colors[row][col])

plt.show()
```

### Actual outcome

The output is equally sized subfigures without any space between them and the full extent being used despite the input restrictions.

### Expected outcome

What is expected is a properly spaced areas with the proper extent. This can be produced when using `add_subplot` instead of `add_subfigure`.

### Additional information

_No response_

### Operating system

_No response_

### Matplotlib Version

3.8.3

### Matplotlib Backend

_No response_

### Python version

3.12.2

### Jupyter version

_No response_

### Installation

conda

Start by running the provided Python reproduction with Matplotlib 3.8.3, then inspect Figure.add_subfigure and its GridSpec handling. Compare the result with Figure.add_subplot and verify that GridSpec extents, wspace, and hspace control the subfigure layout as documented.

Written by the indexing model from the issue text.