[image feature] Too many files open error when image feature is returned as a path
## Describe the bug

PR in context: #3967. If I load the dataset in this PR (TextVQA), and do a simple list comprehension on the dataset, I get `Too many open files error`. This is happening due to the way we are loading the image feature when a str path is returned from the `_generate_examples`. Specifically at https://github.com/huggingface/datasets/blob/508eb4ab5d52f590baa677b4f64b1cc069139f7b/src/datasets/features/image.py#L110, we are open the file handle to the image but never closing it. This in my understanding is causing the issue.

## Steps to reproduce the bug
Pull the PR locally and run the following code
```python
from datasets import load_dataset

dataset = load_dataset("./datasets/textvqa")["train"]
data = [item for item in dataset]

# Error happens
```

## Expected results

List comprehension should work smoothly

## Actual results

`Too many open files error`

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 2.0.1.dev0
- Platform: macOS-12.2-arm64-arm-64bit
- Python version: 3.10.0
- PyArrow version: 7.0.0
- Pandas version: 1.4.1
