Add ability to not automatically copy whitespace-only selections

Nobody has claimed this yet.

Automatic copy to clipboard and clicking in the terminal window combine to overwrite the contents of the clipboard with some whitespace or a single character, far too often/easily.

I find myself, and I imagine others do as well, accidentally selecting something when clicking into the terminal to give it focus, which then wipes out whatever I had in the clipboard that I was about to paste. Window's clipboard history allows retrieval, at least, but it's a few extra steps.

I can think of couple possible solutions off-hand:

- When both `copyOnSelect` is enabled, it would be wonderful to have an option to NOT automatically copy whitespace-only and/or single-character selections.
- Just automatically, quietly, don't do white-space only or single-character selections within a short period of the terminal window gaining focus. Getting the exact conditions for this could be tricky; something like "within the first 0.5 seconds of gaining focus, and only the first click/drag (or touch), ignore it".

Either of these options (or something similar) should be basically invisible to the user, functioning to protect mistakes with minimal to no impact upon intentional actions, much like palm rejection in apps/systems does.

No files or tests are named. Start by locating the copyOnSelect setting and the terminal selection-to-clipboard behavior, then determine how focus-related selections are handled. Done means whitespace-only or single-character accidental selections no longer overwrite the clipboard while intentional selections still copy.

Written by the indexing model from the issue text.