debug: add crate features which enable egui DebugOptions

--features debug-widget-callstack
  Show callstack for the current widget on hover if all modifier keys
  are pressed down

--features debug-interactive-widgets
  Show an overlay on all interactive widgets

Notes:
- debug-widget-callstack asserts `egui:callstack` feature when enabled
- Only works in debug builds, compile error w/ release builds

Cargo.toml

@@ -67,6 +67,8 @@ security-framework = "2.11.0"
 [features]
 default = []
 profiling = ["puffin", "puffin_egui", "eframe/puffin"]
+debug-widget-callstack = ["egui/callstack"]
+debug-interactive-widgets = []
 
 [profile.small]
 inherits = 'release'