Polar plot label rotation ignored

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### Bug report

**Bug summary**

In matplotlib 2.0.2 you could rotate the axes labels on a polar plot, just as with any other plot

```python
for i, label in enumerate(ax.get_xticklabels()):
label.set_rotation(i*90)
```
This is not possible anymore with matplotlib 2.2.2

**Code for reproduction**

```python
import matplotlib
import numpy as np
import matplotlib.pyplot as plt

fig=plt.figure(figsize=(4,3))
ax = plt.subplot(111, polar=True)
ax.set_xlabel("Matplotlib "+matplotlib.__version__)
ticks = np.arange(3)*np.pi/2.
labels = ["".join([a]*5) for a in list("ABC")]

plt.xticks(ticks, labels, size=16)
for i, label in enumerate(ax.get_xticklabels()):
label.set_rotation(i*90)

plt.tight_layout()
plt.show()
```

**Actual outcome with matplotlib 2.2.2**

The rotation of the labels is simply ignored.


**Expected outcome (as with 2.0.2)**

We would expect to see the labels rotated as in this plot, produced by the same code run on matplotlib 2.0.2.


Start by running the provided polar-plot reproduction script with matplotlib 2.2.2 and inspect how polar axes create and draw their x tick labels. Done means label.set_rotation(i*90) visibly affects the labels as it did in matplotlib 2.0.2, without breaking the shown plot behavior.

Written by the indexing model from the issue text.