Implement dev mode options

[TokisanGames]

Begining of some options in #835

• Added an option to disable the instancer
• Added rudimentary readonly mode. Currently it only sets a flag, which the editor_plugin.gd uses to disable cursor input
• Added an option to disable color_map generation in VRAM. Still writes and saves data. Partial Add an option to disable the color map, to save ram/vram #379

Pending:

• If color_map is disabled, then at game run time free the maps from the regions to save RAM.
• In read_only mode:
  • have Terrain3DInstancer and Terrain3DEditor early exit on Operating. We'll leave the API, just no hand editing.
  • disable the tool bar and asset dock.
• Add placeholder mode that replaces all meshes with AABB sized cubes and enable highlight
• Add command line option for dev_mode
• Add dev_mode placeholder (no color map, placeholder instances), saver (no color map, no instances, autoshader?)

[aidandavey]

Does hiding the MMI parent change the VRAM allocation, or only skip the draw calls? What if we instead destroy the MMIs and skip rebuild to 'hide' them? That should save RAM, VRAM, avoid processing the MMIs and avoid the draw calls.

In the Node to RS version there will be no MMI parent to hide, so would need to take the above approach anyway.

[TokisanGames]

Does hiding the MMI parent change the VRAM allocation, or only skip the draw calls?

show_instances turns off visibility of the MMI nodes
instancer_mode = disabled destroys and prevents creation of the MMIs.

The latter saves ram and vram. The former will go away with your RS version. Transforms still update in either case.