Implement Drag-and-return & Circular drag

[feathecutie]

This implements drag-and-return and circular drag functions inspired by MessagEase.
These functions were essential to my workflow before I switched to thumb-key, so I figured I'd reimplement them here.

I'm sure some parts of the code could be improved, and I don't really like the implementation detail of having to pass the additional keys of the other keyboard layers to each key (as secondaryKey and tertiaryKey), but this seems like the easiest implementation with regard to the current architecture of thumb-key.

Drag-and-Return

Lets you drag in direction of one the edges/corners of a key and back to the center in order to send the key on that edge/corner in the opposite case, so uppercase if the keyboard is currently lowercase, or lowercase if the keyboard is currently uppercase.
Note that this technically just switches between the main and shifted keyboard layout, so it will just send whatever is at the corresponding position of the equivalent keyboard.

Circular drag

Lets you drag in a circle starting and ending on the same key in order to send either the center key in the opposite case (main vs shifted layout), or send the number at the corresponding position of the key (numeric layout).

The circle detection code is completely improvised and could probably use some improvements, but in my testing, both drag-and-returns and circular drags were detected almost flawlessly.

[feathecutie]

Nevermind, I just saw #362 and #317. I will leave this PR open for review/comment, but I understand that complex gestures are outside of the design of thumb-key.
In case this does not get implemented, I will probably just keep using a personal fork of thumb-key for now.

[mpsijm]

Thank you so much for implementing this! I've been missing this feature ever since I switched away from MessagEase, but hadn't found the time yet to implement it myself 😄

I have the feeling that the gestures are sometimes quite "strict". It happens to me quite often that a circle is interpreted as a drag-and-return, unless I try really hard to draw a perfect circle. Or, for the drag-and-return: if the return-part of my gesture overshoots the original key, the opposite letter gets typed (for example, when I want to type capital U, I get a lowercase d instead, because my return gesture moves too far downwards).

I'm not quite sure how to improve this, but if it helps, I can attach a debugger to my phone to try out some gestures, so we can link the recorded positions to expected results, to build a (unit-)test set 🙂

[dessalines]

Thx! Everything works pretty well, except the circle-and-drag is very touchy.

[dessalines]

LGTM. Do you want to try tweaking the circle-and-drag now, or do that later?

[feathecutie]

LGTM. Do you want to try tweaking the circle-and-drag now, or do that later?

I don't really have time for it right now, so the earliest I'd commit something regarding that is tomorrow.

[dessalines]

Up to you, its no rush obvi.

[dessalines]

The DB stuff is good here, and we can always tweak later. Thx a ton for this!