clang-format RemoveBracesLLVM should handle else block containing an if block

[owenca]

The RemoveBracesLLVM option doesn't remove the braces of an else block that contains a single if statement when the body of the if statement is a block:

$ cat test.cpp
void f() {
  if (a1)
    f1();
  else {
    if (a2)
      f2();
  }

  if (a3)
    f3();
  else {
    if (b) {
      g();
      h();
    }
  }
}
$ clang-format -version
clang-format version 15.0.0 (https://github.com/llvm/llvm-project 09865ae95dbf0322bbf3e7b3847b2b11373a0297)
$ clang-format -style="{InsertBraces: true, RemoveBracesLLVM: true}" test.cpp
void f() {
  if (a1)
    f1();
  else if (a2)
    f2();

  if (a3) {
    f3();
  } else {
    if (b) {
      g();
      h();
    }
  }
}

Expected output:

...
  if (a3) {
    f3();
  } else if (b) {
    g();
    h();
  }
...

[llvmbot]

@llvm/issue-subscribers-clang-format

[owenca]

https://reviews.llvm.org/D127260