[Bug]: bbox and alignment issues with math text

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### Bug summary

There are several issues with bbox and text alignement when math is used, as evidenced in the mwe below.

In the 'normal' case (1st line), all is ok.

When using mathtext (2nd), the height of the bounding box depends on the text contents while it should not (no fancy super/under script that would extend beyond 'lp'). Also note that the horizontal alignment is different wrt the 1st and 3rd lines (space to the left of the V, no space to the right of the last letter).

When using 'usetex' (3rd line), the bounding box seems correctly placed, but the text position itself in the second case is off by a little bit (see the 'l' being slightly above the line).

### Code for reproduction

```python
import matplotlib.pyplot as plt

kw = dict(
fontsize=55,
bbox=dict(boxstyle='round,pad=0', fc='lightsteelblue', ec='none')
)

plt.annotate('V lp', xy=(0.2, 0.7), **kw)
plt.annotate('V l', xy=(0.5, 0.7), **kw)
plt.axhline(y=0.7, zorder=10)

plt.annotate('$V$ lp', xy=(0.2, 0.4), **kw)
plt.annotate('$V$ l', xy=(0.5, 0.4), **kw)
plt.axhline(y=0.4, zorder=10)

plt.annotate('$V$ lp', xy=(0.2, 0.1), usetex=True, **kw)
plt.annotate('$V$ l', xy=(0.5, 0.1), usetex=True, **kw)
plt.axhline(y=0.1, zorder=10)

plt.show()
```

### Actual outcome


### Expected outcome

2nd row: the height of the first bbox should be fixed.

3rd row: the vertical positioning of the text in the second case should be fixed.

### Additional information

_No response_

### Operating system

_No response_

### Matplotlib Version

3.5.1

### Matplotlib Backend

QtAgg

### Python version

3.10.2

### Jupyter version

_No response_

### Installation

_No response_

Start by running the provided Python reproduction with Matplotlib 3.5.1 and compare the three annotation rows. Trace the annotation, text-layout, and mathtext bounding-box handling used by the reproduction; done means mathtext produces a fixed expected bbox and the usetex text is vertically aligned consistently.

Written by the indexing model from the issue text.