Make middle-click do copy-and-paste in integrated terminal

[lhmouse]

Maybe this is a dup of #26902.

The traditional mouse button for copy-and-then-paste on Linux is the middle button, while it is the right button on Windows. However, the notable MSYS2 terminal emulator, mintty, which is also utilized by the Git Bash, defaults to the linux configuration (but it's configurable). As a dual-platform user, having to be aware of this divergence is really a pain. Thus, I suggest we make this configurable, as I am more accustomed to the middle button.