Fix Warp mouse on Tablet/Trackpad 3D Navigation Scheme

[MaxiSanc37]

Fixes_mouse_warp.mp4

(the lag in the video is not reflective of how the engine is running, it's just the windows snipping tool doing some weird cuts on the video).

This fixes #116177 where emulated 3-button navigation (e.g. Alt/Shift + trackpad drag) stopped when the pointer left the 3D viewport. Instead of relying on mouse capture (which hides the cursor), this PR adds an emulated-nav continuation path in Node3DEditorViewport:

• tracks whether emulated navigation is active,
• computes active emulated nav mode from current modifier shortcuts,
• temporarily enables global input() processing while emulated nav is active,
• applies nav updates from outside-viewport motion there,
• disables that path when modifiers/nav mode are no longer active.

Inside-viewport motion still uses the existing _sinput() flow, so behavior remains consistent and avoids double-processing.

Changed files

• node_3d_editor_plugin.h
• node_3d_editor_plugin.cpp

Testing

• Emulated 3-button trackpad nav continues when crossing viewport edges.
• Cursor remains visible.
• Standard navigation and freelook behavior remain unchanged.

[MaxiSanc37]

I accidentally created this feature branch from a previous PR feature branch so there's also the code that was changed for that issue: #115915 so the code insertions for that is included as well, do you want me to remove the changes on that file manually and squashing the commits?