Written/sounding pitch switch, part 2

[avvvvve]

Continued from @rpatters1's PR #24784 which resolved #15594

UI changes to make

NOTE: Design for this section is in progress

We're going to move this feature out of the playback bar and make it a preference in the 'Note input' section.

We'll provide at least one of the following additional ways to access it:

• Placement 1: In the piano keyboard context menu
• Placement 2: As a sub-option of "Concert pitch" in the bottom bar
  • This might be solved by changing the checkbox to a button triggering a popup containing both...
    • the (existing) option to display the score in concert pitch (which is linked to an option in Style > Score) and
    • this new feature

While we're looking at the playback bar context menu, we may make "Enable MIDI input" an option available in the 'Audio & MIDI' section of Preferences.

Existing implementation (to be changed)

[avvvvve]

Just filed #26493 to address the functional issue of keyboard entry not working with this feature. UI changes can come later.