Use document language for note names

[jocelyn-stericker]

From @chris-morgan:

I always use \language "english", but tools like Change Key Signature don’t respect that, still writing fis and ges for F♯ and G♭ rather than fs and gf.

See define-note-names.scm for the current supported languages and how to write notes in that language. Here’s a simple regular expression for detecting the language: /\\language "(nederlands|catalan|deutsch|english|espanol|italiano|norsk|portugues|suomi|svenska|vlaams)"/.