Make space shortcut for selection mode view-local instead of global

Before this commit, the "Space" keyboard shortcut was bound to
triggering selection mode by default. After this commit, pressing
"Space" will only trigger selection mode when the file view area
has keyboard focus.

Pros:
+ Other buttons in the UI can be triggered with Space once again
  just like it is expected from an accessibility point of view.
+ "Type-ahead" searching works once more when typing the space
  char for file names containing such a space char.

Cons:
- "Space" can no longer be used to add the currently underlined
  item to the selection. Instead "Ctrl+Space" needs to be used.
  (However, this is the current status anyway unless a user has
  manually unbound "Space" as a shortcut from Selection Mode.)
- The Selection Mode action will no longer show "Space" as its
  shortcut in menus.

Overall, I see solutions to all of these problems, but they seem
over-engineered for the issues they are trying to solve, so I
believe this somewhat small commit is the best solution for now.

BUG: 458282
BUG: 458281
CCBUG: 463048
FIXED-IN: 23.04


(cherry picked from commit 44c82a16)