Scroll instruments list with Y+D-pad

[prayerie]

Inspired by #118 (although it doesn't do anything nearly as drastic as reworking tobkit to support focusing).

The Y button is currently unused, and it's common for trackers to include shortcuts to easily scroll up and down the instrument list, without use of the computer mouse.

Y+Up and Y+Down move up and down, respectively (no wraparound).

Holding B during this operation moves in units of four rows instead of one, in the same manner as the pattern editor.

Y+R+Up jumps to the top of the instrument list. Y+R+Down, however, does not jump to the bottom, as it is ambiguous as to whether it should jump to the maximum scrollable instrument slot (always 0x7f, or 80), or the last populated instrument.

[prayerie]

ignore the force pushes i kept accidentally including code that i didn't mean to pr lol

[deadpahn]

Cool! So does it still audition the audio when it moves?

[prayerie]

(#139 i reopened the pr here hehe)

@deadpahn but no sorry for the confusion, i was simply referencing your issue as similar. this scrolls the instrument list on the right and doesn't audition the instrument each time (as trackers do not tend to do this)

although i do plan to do this for the sample browser too, although it would involve reworking the ui toolkit to support focus as asiekierka already said in your issue (or use some other key combo)

[prayerie]

@deadpahn if you are able/cba to test this: build artifact if it's good i might change my pr (in essence y+dpad scrolls the file browser if the file browser tab is active, otherwise it scrolls the inst list, and if a sample is selected it auditions it, kind of a clunky implementation but precludes having to rework tobkit to support focusing)