fix: `partition_pdf()` removes spaces from the text (#3106)
Closes #2896.
This PR aims to fix `partition_pdf()` to keep spaces in text. The
control character `\t` is now replaced with a space instead of being
removed when merging inferred and embedded elements.
### Testing
PDF:
[rok_20230930_1-1.pdf](https://github.com/Unstructured-IO/unstructured/files/15001636/rok_20230930_1-1.pdf)
```
elements = partition_pdf(
filename="rok_20230930_1-1.pdf",
strategy="hi_res",
)
print(str(elements[20]))
```
**Results:**
- PR
```
Name of each exchange on which registered New York Stock Exchange
```
- main branch
```
Nameofeachexchangeonwhichregistered NewYorkStockExchange
```