clang-format: support aligned nested conditionals formatting

When multiple ternary operators are chained, e.g. like an if/else-if/
else-if/.../else sequence, clang-format will keep aligning the colon
with the question mark, which increases the indent for each
conditionals:

  int a = condition1 ? result1
                     : condition2 ? result2
                                  : condition3 ? result3
                                               : result4;

This patch detects the situation (e.g. conditionals used in false branch
of another conditional), to avoid indenting in that case:

  int a = condition1   ? result1
          : condition2 ? result2
          : condition3 ? result3
                       : result4;

When BreakBeforeTernaryOperators is false, this will format like this:

  int a = condition1 ? result1 :
          condition2 ? result2 :
          conditino3 ? result3 :
                       result4;