Change ObjectInspector to work via object selection

[Givikap120]

Known issues:

• Taiko selected objects are appearing as "deselected" when scrolling back earlier than half of the playfield
• Taiko selected objects are appearing as "deselected" after time it should be hit (even tho Drawable looks like it's still goes to the left)
• Catch selected objects that were created from nested fruits (slider ends) are fading-in for some reason

First two are most likely because of how pooling in Taiko works
Third is because of some internal catch playfield behavior (didn't found where the fade is applied)

Don't know how to fix the issues, and they're not critical, so waiting on commentary of this situation

[stanriders]

• Do I need to merge STD classes with abstract base as the abstractions isn't used anywhere else?

Yes

• How can I add selection logic to the CatchSelectableDrawableObject and TaikoSelectableDrawableObject without copying? Or I just need to copy it and that's all?

Copying is fine if can't be moved out easily

• Do I need to implement selectable spinner (and other objects without respective difficulty hit objects)?

No

• Selectable object creation can be done with using DrawablePool. But seems to work fine without it. Do I need to do it?

Try running very high object count maps and see how big of a performance hit you get. If it's negligible and your system is more or less average it should be fine I think

[Givikap120]

Known issues:

• Taiko selected objects are appearing as "deselected" when scrolling back earlier than half of the playfield
• Taiko selected objects are appearing as "deselected" after time it should be hit (even tho Drawable looks like it's still goes to the left)
• Catch selected objects that were created from nested fruits (slider ends) are fading-in for some reason

First two are most likely because of how pooling in Taiko works
Third is because of some internal catch playfield behavior (didn't found where the fade is applied)

Don't know how to fix the issues, and they're not critical, so waiting on commentary of this situation

[smoogipoo]

In general we don't #nullable enable in new files.

[stanriders]

I'm planning to go over the whole project and enabling nullables everywhere after I'm done refactoring this pr