[clang-reorder-fields] Reorder leading comments (#123740)
Similarly to https://github.com/llvm/llvm-project/pull/122918, leading
comments are currently not being moved.
```
struct Foo {
// This one is the cool field.
int a;
int b;
};
```
becomes:
```
struct Foo {
// This one is the cool field.
int b;
int a;
};
```
but should be:
```
struct Foo {
int b;
// This one is the cool field.
int a;
};
```
