Feature request: nano-style click selection

Description

Currently, the only way to select text using the mouse is to drag. This makes text selection with the mouse impossible if you don't have drag support. An example that comes to mind (and the reason for this) is Termux (and possibly, other touchscreens, although I can't say for certain).

There should be an option to change the selection to behave like nano's mark mode.

Basically, nano's mouse selection works like so:

• Double-click (technically, click on the cursor) to enter selection mode. This will be the start (or end if selecting backwards).
• Move the cursor to where you would like to end the selection.
• Double-click (again, technically click on the cursor) to cancel the selection.
• In nano's case, doing an action cancels the selection, although this might not be favorable.

No files or tests are named. Start by tracing the existing mouse-drag selection path and how editor options are defined, then compare the requested double-click start, end, and cancellation behavior with current input handling. Done means the behavior is available as an option and works for touch-oriented selection without breaking existing mouse selection.