message: Document slightly uncommon assignment inside attributes.
  Should be recognized and properly formatted.
  Relevant in the context of
diff: @@ -1848,7 +1848,8 @@ static constexpr FormatterTestCase kFormatterTestCases[] = {
  " logic aaa = expr1;\n"
  " bit b = expr2;\n" // no alignment at '=' yet
  "endmodule\n"},
  - {"module mattr;\n"
  + {"(* foo='{\"bar_.*\"} *)\n" // funny attribute
  + "module mattr;\n"
  "(* attr1=\"value1\" *)\n" // attribute ignored
  "ex_input_pins_t ex_input_pins;\n"
  "(* attr2=\"value2\" *)\n" // attribute ignored
  @@ -1856,6 +1857,7 @@ static constexpr FormatterTestCase kFormatterTestCases[] = {
  "(* attr3=\"value3\" *)\n" // attribute ignored
  "ex wrap_ex ( );\n"
  "endmodule\n",
  + "(* foo='{\"bar_.*\"} *)\n"
  "module mattr;\n"
  " (* attr1=\"value1\" *)\n" // indented
  " ex_input_pins_t ex_input_pins;\n" // aligned
  