Make 3D transforms done inside editor viewport, but w/o grabbing a gizmo handle require pressing alt

[ryevdokimov]

Describe the project you are working on

I figured the PR I made probably needed a proposal.

Describe the problem or limitation you are having in your project

Without this, there is a higher possibility of accidental transforms.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

This would also enable allowing any editor tool to select any node at any time. By requiring pressing alt, the worst that can happen when accidentally clicking/dragging on the screen is selecting another node, which is annoying but harmless. Accidentally transforming can go unnoticed, and cause issue down the road.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

godotengine/godot#87756

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

N/A

Is there a reason why this should be core and not an add-on in the asset library?

N/A