Make Image.get_size() return a Vector2i instead of a Vector2

[samdze]

Closes #62856

[fire-forge]

The documentation needs to be updated too:

godot/doc/classes/Image.xml

Lines 252 to 253 in d26442e

	<method name="get_size" qualifiers="const">
	<return type="Vector2" />

[samdze]

Done!

[clayjohn]

get_size() is used throughout the codebase. This should likely be accompanied by a review of where it is being used and those uses should be updated to Vector2i/Size2i as well

[reduz]

This is good on its own, but we need to check other simliar places in the codebase that are pre Vector2i

[akien-mga]

Thanks!

[fire-forge]

This is good on its own, but we need to check other simliar places in the codebase that are pre Vector2i

@reduz I did the rest of the Image and ImageTexture methods in #62871. I'm sure there are many other places that need conversion, but I haven't found any yet.