[hh_ht11xx] add new driver for keychain 55 in 1

[Figur8]

also some code clean up

[felipesanches]

I'd like to inform that this is the first PR of Ismael (@figure8), one of the 3 people I am offering some mentoring on MAME development.

The content of this PR was authored by both of us, as we've prepared it on a video call conversation in which I explained to him many aspects of how the code is organized. I hope I can help his journey into MAME development to be smoother, by offering that kind of support.

Having said that, there are a few aspects of this PR that may be a bit controversial, so I'd like to get feedback on how to do it properly.

There are a few input names that are now in all caps because that's how they're depicted (as silkscreen labels) on the handheld.
We were a bit unsure about that, but we considered it reasonable to describe it that way. I am not sure if MAME has a specific policy about how to handle that. If needed, we can change them back to lowercase.

Also, the input port names were very confusing with names IN1, IN2 and IN3 while being addressed as m_in[0], m_in[1] and m_in[2] and in reality being called PP, PM and PS. So we believe the refactored implementation is easier to read, specially when cross-referencing with other info about the hardware that we could find online (such as https://github.com/azya52/BrickEmuPy/blob/main/assets/Keychain55in1.brick).

You can count on both me and @Figur8 to swiftly address any other issues in this PR, as we'd like to help Ismael to become a regular contributor to MAME.

[felipesanches]

Here's a photo of the real device:

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And at https://github.com/azya52/BrickEmuPy/blob/main/assets/Keychain55in1.svg there's an SVG that could in the future help us in preparing a .lay file for this handheld: