Fix variable and setting nodes not updating on type change

[Atlinx]

Fixes #2067
Fixes #2062 (Uses the proposed change in the issue)
May also fix #2063 , since I suspect a null value might be the product of the visual editor not generating the correct code

Changes

• Made _value_type reset the value and force an editor refresh on change
  • Solves the issue of Set var node not updating timeline when set value type is changed.  #2067 where changing the value type does not reset the value
• Refactor event_variable and event_settings to use enums for their different value types to make the code easier to read
• Refactor event_block to not call set_value on fields that are not visible. This prevents invisible fields from throwing errors when they get injected with the wrong data type in event nodes that have varying value types (such as event_variable and event_settings, whose value types can be strings, numbers, expressions, etc.)

[Jowan-Spooner]

Added a tiny comment. Looks great otherwise. I want to take a moment to actually test this and don't have the time right now (will hopefully get to it later or tomorrow), but it looks really good. Thank you so much already.

[Jowan-Spooner]

This seems to work perfectly. Thank you very much!