[clang] [clang][AST] Pretty-print default template template args (PR #162134)

[Andrey Ali Khan Bolshakov via cfe-commits]

https://github.com/bolshakov-a commented:

@erichkeane, @cor3ntin, @mizvekov

The changes suggested by formatter would cause the `TestClassTemplateDecl9` test case to stand out from the neighboring test cases, which use 4-symbol indentation. Should I apply them or put `// clang-format off`? 

https://github.com/llvm/llvm-project/pull/162134