[Bug-Candidate]: Consider non-ASCII when source mapping

### Describe the issue:

Hey!

Just noticed that `source_mapping` will be misaligned when a `.sol` file containing non-ASCII is opened. Maybe "misaligned" isn't the correct phrasing as it depends on how the `.sol` file is opened in Python. If I open [like in Slither](https://github.com/crytic/slither/search?q=open%28) and [Crytic compile](https://github.com/crytic/crytic-compile/search?q=open%28), a normal read with `encoding=utf-8` it will be misaligned, but it works fine reading it as bytes (`rb`).

Not sure if this has any implication on Slither itself, but might be handy to know when trying to slice the source based on Slither output.

### Code example to reproduce the issue:

```python
from slither.slither import Slither

# Write simple test contract with non-ASCII
with open('test.sol', 'w') as sol:
sol.write(
'''
// 有趣的 // <- will cause shift with utf-8 read as in bytes this is \xe6\x9c\x89\xe8\xb6\xa3\xe7\x9a\x84
contract A {

uint public x;

constructor() public {
x = 1;
}

}
'''
)

# Parse with Slither
slither = Slither('test.sol')

# Open file with utf-8 as done in Slither and print contract positions
with open('test.sol', encoding='utf-8') as sol_file:
source_code = sol_file.read()
contract_mapping = slither.contracts[0].source_mapping
start, end = contract_mapping['start'], contract_mapping['start'] + contract_mapping['length']
print(source_code[start:end])
```
Will print the incorrect part of the source code:

```solidity
ct A {

uint public x;

constructor() public {
x = 1;
}

}
```

Can change it to binary read and then decode and it looks fine:
```python
with open('test.sol', 'rb') as sol_file: # read binary
source_code = sol_file.read()
contract_mapping = slither.contracts[0].source_mapping
start, end = contract_mapping['start'], contract_mapping['start'] + contract_mapping['length']
print(source_code[start:end].decode('utf-8')) # decode binary
```
Will print:

```solidity
contract A {

uint public x;

constructor() public {
x = 1;
}

}
```

### Version:

```yaml
Slither: 0.8.2
```

### Relevant log output:

_No response_