Fix blurred content of embedded windows

[scgm0]

Fix #54030
I honestly don't know if I'm doing it the right way, but the issue seems to be forgotten and after a flurry of attempts I'm getting good results.
before:

after:

example:
embedded-window.zip

[hsvfan-jan]

In the screenshot, the circles of Test2 and Test3 seem to have become an octagon (the newly introduced white outline probably making it a full circle I'd assume)

[scgm0]

In the screenshot, the circles of Test2 and Test3 seem to have become an octagon (the newly introduced white outline probably making it a full circle I'd assume)

It seems to be a problem caused by viewport_set_global_canvas_transform. I don’t know where the specific problem is.

[scgm0]

In the screenshot, the circles of Test2 and Test3 seem to have become an octagon (the newly introduced white outline probably making it a full circle I'd assume)

When I manually assign the radio_unchecked icon in the theme (radio_unchecked.svg was copied from godot), there is no white border around the icon, so maybe the problem is related to the theme cache?