minor tweak in key sig editor - first added accidental aligned to "zero" position

[sammik]

In Custom Key Signatures Editor - now, also firstly added accidental is alligned to its default "zero" position, unless Ctrl is pressed.

(Before, "zero position" was calculated from most left accidental.)

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• [x] I made sure there are no unnecessary changes in the code
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[sammik]

Before, not possible to set offset of first accidental:

https://user-images.githubusercontent.com/1646034/208679433-a3d58a7b-7bfd-4190-aca0-3e02d30a6252.mp4

After, zero taken by default (but also possible to set offset of first accidental):

https://user-images.githubusercontent.com/1646034/208679566-900ba5ae-eacf-4911-af4e-bfde8dd84bcf.mp4

@oktophonie

[RomanPudashkin]

@sammik please rebase

[sammik]

@RomanPudashkin done

[zacjansheski]

Tested on MacOS 14, Windows 11, Ubuntu 22.04.3. Approved