`??` and various improvements

Additions

• [beta] Added null-conditional operators!
  These allow you to do things like instance_nearest(x, y, obj_enemy)?.cur_health ?? 0 instead of assigning result of instance_nearest into a temporary variable, checking that it’s not noone, grabbing cur_health from it, or returning 0 otherwise.

Improvements

• Added #mfunc to auto-completion list.
• Outline View is now better at displaying 2.3 top-level functions.
• Outline View can now display static functions inside constructors.
• Added more settings to Outline View.
• Added a separate keyboard shortcut for folding only #regions (default: Ctrl+Shift+M)
• When the cursor is on JSDoc immediately before a global function, the function will now be highlighted instead of the previous one.
• GMEdit now handles @func JSDoc in GMS2.3 projects.
  I also take a moment to remind you that you should not use @func for hinting methods inside constructors as it adds auto-completion and highlighting items into global scope.

Fixes

• Fixed function name() in Create events not being added to object variable list.
• Fixed var a:Enum = fn() ++a.field (note the missing ;) not using the correct accessor.
• Fixed newly added GMS2.2 resources having their fields inside YYP out of order.
  (didn’t break anything, but IDE would eventually reformat these)
• Fixed freshly created 2.3 objects not being possible to use as a parent until reloading a project.

Misc

• Current theme name is now stored in html[data-theme].
  This allows to set theme-specific rules in project-specific CSS.
• Keyboard shortcuts menu now supports descriptions (shown as mouseover text).
• Updated the GMLive.js build to handle editing-related logic on GMEdit side of code.
  (hopefully nothing should be different)

Stable channel has everything up until null-conditional operators.