Make mouse input handling more consistent in the editor

[vitorbalbio]

Describe the project you are working on:
Space Tactical RPG https://twitter.com/ZeroPointGame

Describe the problem or limitation you are having in your project:
This proposal is part of a much more complete UI/UX overhaul and should be considered with this view about Godot Editor problems and Suggestions: #1503

Inconsistent Mouse Events

There's bad inconstancy with the current Mouse Actions between the FileSystem and the Scene Panels. Consistency and predictable behaviors is one of the most important UX Principles so this should be fixed if possible.

FileSystem:
Click (Mouse Press) - Select and Show Import Options
Click on Already Selected Element - Do Nothing.
Double Click - Open Asset, Scene, Script etc...
Drag and Drop - Works for Drop files in the Viewport and Inspector as Resources. Should reorder on list but do not work because list is always alphabetical sort.

Scene:
Click (Mouse Press) - Select and Show Inspector/Node Options
Click on Already Selected Element - Rename.
Double Click - Do Nothing.
Drag and Drop - Do Nothing.

The main problem i see here is the Mouse Click event is not correctly used/implemented in Godot.
Don't know the reason but Mouse Press is used as Mouse Click in Godot Editor! It limit how much different events it can handle. Click should be a sequence of Mouse Press - Check Max Threshold Mouse Move - Mouse Release. If Moved too much it's a Drag Event not a Click. The Event should only be accepted as a Click in the Mouse Release not before.

Double Click is a Click - Check time Threshold event. Don't know how it's implemented now.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:

With this new Click event implemented this is my proposal:

FileSystem
Click (Real Click) - Select and Show Import Options
Click on Already Selected Element - Rename. [NEW]
Double Click - Open Asset in Inspector, Scene, Script etc...
Drag and Drop - Works for Drop files in the Viewport and Inspector as Resources.

Scene:
Click (Real Click) - Select and Show Inspector Options
Click on already selected element - Rename
Double Click - Do Nothing.
Drag and Drop - Can Drag and Drop in Exported Notepath fields in Inspector. [NEW] Since the Click is now a different event of the Drag and Drop it will not change the current Inspector Selected so it will works as should.

If this enhancement will not be used often, can it be worked around with a few lines of script?:
Will be used often.

Is there a reason why this should be core and not an add-on in the asset library?:
It's a core editor feature.