Added: Add right-alt-workaround property

[fitzsim]

This fixes the issue discussed in
#4327 for me.

When using my Bluetooth hardware keyboard, I would like right_alt to function like left_alt for Readline-style input (for example, word traversal with right_alt + f and right_alt + b). This patch adds a workaround boolean to support that.

I tested it on a Pixel 8 running GrapheneOS, Android version 17.

If this looks OK then I can submit a comment patch for termux.properties to https://github.com/termux/termux-tools.

I will leave this as a draft for now because I still want to understand the default behaviour of right_alt + b with a hardware keyboard. On my configuration, every right_alt + <key> combination makes the context menu flash briefly then disappear, which seems like a bug. If so, maybe I should first try to fix the default right_alt behaviour.