[Clang][CodeGen]Beautify dump format, add indent for nested struct and struct members

Beautify dump format, add indent for nested struct and struct members, also fix test cases in dump-struct-builtin.c
for example:
struct:
```
  struct A {
    int a;
    struct B {
      int b;
      struct C {
        struct D {
          int d;
          union E {
            int x;
            int y;
          } e;
        } d;
        int c;
      } c;
    } b;
  };
```
Before:
```
struct A {
int a = 0
struct B {
    int b = 0
struct C {
struct D {
            int d = 0
union E {
                int x = 0
                int y = 0
                }
            }
        int c = 0
        }
    }
}
```
After:
```
struct A {
    int a = 0
    struct B {
        int b = 0
        struct C {
            struct D {
                int d = 0
                union E {
                    int x = 0
                    int y = 0
                }
            }
            int c = 0
        }
    }
}
```

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D122704