clang-format: [Proto] Use more compact format for text-formatted options

Before:
  enum Type {
    UNKNOWN = 0 [(some_options) = {
      a: aa,
      b: bb
    }];
  };

After:
  enum Type {
    UNKNOWN = 0 [(some_options) = {a: aa, b: bb}];
  };

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@273553 91177308-0d34-0410-b5e6-96231b3b80d8