fix #26746: German chord mode compatibilty with 1.3

As discussed in issue thread - all changes referring to German note spelling mode:

- fix bug preventing German spelling mode from being recognized initially on load of 1.3 score
- change default rendering of TPC_B_B from B to Bb (reverting to 1.3 behavior even for new scores)
- edit legacy chord description files to override default spelling of flat and sharp, so scores created in 1.3 using German spelling will keep 1.3 rendering of "b" and "#" while new scores will get "es" and "is"