[clang][Diagnostics] Add bitfield source range to zero width diags (#68312)

Before:
```
array.cpp:157:8: error: named bit-field 'a' has zero width
  157 |   char a : 12 - 12;
      |        ^
1 error generated.
```

After:

```
array.cpp:157:8: error: named bit-field 'a' has zero width
  157 |   char a : 12 - 12;
      |        ^   ~~~~~~~
1 error generated.
```