Add more keys to "key pressed" dropdown

[towerofnix]

The "key pressed" dropdown is missing some keys that make it lack a lot of potential.

While keys like "control" and "command" are best left out because they have browser behavior, the following keys don't mess with the browser, and would be useful for typewriter (custom input) and game projects:

• Shift (Useful general-purpose modifier key. No browser behavior.)
• Enter (Frequently used for selecting options in keyboard-based UI.)
• Backspace (Useful in typewriter projects or as a "back" button.)

[thisandagain]

/cc @ericrosenbaum @kchadha

[TongDaDa]

It is useful

[towerofnix]

I've updated the issue description with a proper list of keys I think would be useful (more welcome if anyone has ideas!).

[AmazingMech2418]

I recently submitted a PR to add the backspace and shift keys. The enter key is already supported.

[griffpatch]

Not being able to use backspace has been a real step back for any text input based projects that are using anything other than the 'ask' block. I'd certainly vote up the request to add a backspace character to the dropdown... if not at least support detecting it the old way using the ascii backspace char! (drop down prefered)

[apple502j]

@griffpatch The old way breaks Scratch 3.0's XML parsing. It cannot handle Backspace unicode char.
Backspace dropdown is possible.