[3.2.1] Mouse clicks not registering if click happened outside button

[DoctorWhoof]

Godot version:
3.2.1.stable.oficial

OS/device including version:
MacOS 10.15.4 and Windows 10

Issue description:
I'm trying to create an UI where the user can click on a button, then DRAG the mouse over the neighbor buttons, without releasing the left button, to toggle their state.

However, it only works for me on Windows and MacOS if I drag the mouse OUT of the window, then back into it. A user on Linux has reported that it works as expected.

My minimal repro script stores the state of mouse clicks, then uses an "_on_mouse_entered" signal to print a message, but only if the user has already clicked and is dragging.

Steps to reproduce:
Run the minimal project attached. CLICK on a button, and without releasing the left mouse button, DRAG over the neighbor buttons. You should see the "button is drag-pressed!" message printed for each button.

Minimal reproduction project:
Drag-Click Test.zip

[swenner]

I can confirm that it is also broken on Debian GNU/Linux (Gnome) with Godot 3.2.2beta. You have to move the mouse outside of the window to get the mouse entered event. Could be related to #20881

[DoctorWhoof]

It definitely seems related to #20881. I did some more testing, and the individual buttons can register the "click" just fine when it happens outside their rect (I added a "print"statement to verify it). It's the mouse_enter event that seems to not be working as expected, as far as I can tell. Thanks!

And just in case someone is wondering why this is useful, you can use buttons that behave like that to:

• Mass toggle the state multiple items, like the Layers in Photoshop, without RSI inducing click-click-clicking on each one
• Play a sound for each key on a piano roll without releasing the mouse button
• Make "toddler friendly" UI's (click dragging can be easier than multiple clicks in some situations) in apps for kids, etc.

Thanks!

[Calinou]

Duplicate of #20881 (same cause).