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;
};
```
Currently, trailing comments get mixed up:
```
struct Foo {
int a; // This one is the cool field
// within the struct.
int b;
};
```
becomes:
```
struct Foo {
int b; // This one is the cool field
// within the struct.
int a;
};
```
This should be:
```
struct Foo {
int b;
int a; // This one is the cool field
// within the struct.
};
```