Allow linked reminders for different medicine

[Arkonos]

This PR aims to allow the user to select a different medicine (B) for the linked reminder than (A) that of the parent reminder.
This would fulfil the original ask of #131 more closely.

When creating a linked reminder, the user will first be prompted to select one of the existing medicines from medicineRepository.medicines. This list includes all, including A, but does not offer the custom field. Then the dose and delay have to be entered as before.
As the user will still be at the medicine A and not see the new linked reminder, a toast message will inform about the creating of the same. The linked reminder can be seen edited in medicine B.

Since I am not familiar with Kotlin or Java, everything has been coded by AI so far.
I've tested it in an emulator and it works. Before investing more time, I wanted to ask if you're generally in favour of this approach.

Some questions for you

1. I wanted to keep the changes to a minimum so far, so I'm reusing ManualDose functionality. Since the list of existing medication is now used in two different places, do you want me to create a separate module instead?
2. Do you want an indicator in the parent reminder that a linked one exists?
3. So far, there's no warning before deleting a parent reminder with a link. Given that a relationship is now reaching across more than one view, do you think this is necessary? The same would apply to deleting medicine A as a whole.
4. Do you want me to change the toast message to a clickable one, leading the user to B? I don't know how much more complex that'd be.

My personal use case is actually the same medication, but in a different dose. Since there are two different pills, I need to track the stock separately. With this PR, I can create Medication A 5 mg and Medication A 10 mg and use a linked reminder.
Having it under one medication would be cleaner, but would probably mean a lot of work.

[Futsch1]

@Arkonos Thanks a lot for your contribution, and also thanks for disclosing that you used AI!

1. I like it that you used the existing code. In terms of clarity, it would be very welcome to create a separate module that hosts the logic to create medicine selection lists and that is then used by both use cases in the manual dose and the linked reminder.
2. This would be a great addition, but not necessary to merge the PR from my point of view.
3. Same here, this might be rather seen as an optimization. Maybe create an issue for 2. and 3. to implement this later/separately.
4. No, that is fine as it is.

One thing that keeps the PR from being merged is the fail of the tests, which are due to the additional UI interaction required when creating linked reminders. Please have a look at the androidTests that run there and fix them accordingly. Note: In order to run them locally, you need to set the date/time of the device to 1.8.25, 16:00 (or use the adb command adb shell su 0 toybox date 0801160025). If you have issues getting the tests to work, let me know and I can support you.