Add missing initializer_list constructor to TypedDictionary

[tomfull123]

Noticed while adding initializer_list support to godot-cpp godotengine/godot-cpp#1750

This PR adds initializer list support to dictionarys for object and refcounted types, less useful in Godot, but will be very useful in gdextensions, it just needs to get merged here first.

After this PR goes in, I also want to add support for object and refcounted types as dictionary keys, this PR currently only supports them as values.

[tomfull123]

Originally added in #99751
Looks like it was just overlooked?

[AThousandShips]

We should probably add tests for this like there are already for standard Dictionary, to ensure it works as expected

[tomfull123]

We should probably add tests for this like there are already for standard Dictionary, to ensure it works as expected

Added some tests

[Repiteo]

There doesn't need to be a separate typed dictionary test file; typed tests already happen in the normal dictionary file, so those can be relocated there instead

[tomfull123]

There doesn't need to be a separate typed dictionary test file; typed tests already happen in the normal dictionary file, so those can be relocated there instead

I thought it would be nicer to have tests for each class in their own test file, but no worries, I've moved them into the dictionary test file

[Calinou]

Code and tests look good to me.

[Repiteo]

Looks good!

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉