[INTEGRATED-TERMINAL] Clear selection by pressing escape key

[ddruker]

Overview

This PR will add a command that prevents the terminal window from placing the terminal prompt in view when the escape key is pressed and there is output selected.

Ref Microsoft/vscode#46728

Screenshots

• The user can select and when escape is pressed, it will clear the selection. When there is no selection, it will default to normal behavior.

[Tyriar]

@ddruker looks good! I commited a change to make the action name more consistent with the rest and also cover the case where the find widget is visible: when both the find widget and a selection is up, escape will close the find widget, another escape will clear the selection, another escape will send esc to the shell.