Implement inactive properties

[MarcusElg]

An attempt to implement godotengine/godot-proposals#4823.

Currently an early draft to start the discussion. Imo some solution for dependent properties would improve the usability a lot, as it's currently a bit confusing what properties have an effect, and which don't. Currently it's implemented using a new PROPERTY_HINT that is changed in validate property, should a separate method like suggested in the proposal be used instead?

TODO:

• Fix errors
• Support translation Done
• Use a custom theme colour for invalid properties Done
• Decide visuals
• Decide which properties to use this on
• Expose to gdscript tool scripts?

[MarcusElg]

I've implemented a custom theme colour for inactive properties, should it be some sort of gray or some shade of yellow like warnings usually are? Yellow might me a bit too much tho.

[MarcusElg]

@KoBeWi The issue with using a custom propertyhint as you suggested in the proposal is that it can only have one at the time, so as you see in the image above it looses it's suffix as well as min/max values etc. So maybe it's more logical to have it as a propertyusage instead? In that case there would have be a separate warning value for properties as propertyusages don't have any extra data.

[MarcusElg]

I've changed it to be a propertyusage instead so now it's ready for some feedback

[KoBeWi]

Looks good overall, but I'm not convinced about adding another member to PropertyInfo (the property_dependency). I wonder if it couldn't be part of hint_string, like just add it after some semicolon to the existing hint or something.
And if not, PROPERTY_USAGE_INACTIVE is kind of redundant, because you can just check whether property_dependency is not empty.
Need some feedback from @godotengine/core team.

[MarcusElg]

@KoBeWi have you discussed anything more regarding this?

[KoBeWi]

Not really. I forwarded this PR on RocketChat, you can join to discuss it (it would be faster than waiting for a comment in the PR).

[Geometror]

I think inactive properties should be colored gray, yellow clashes with properties of editable children (see #53260)