Font breaks when using oversampling and theme overriding on a viewport

[ace24713]

Tested versions

3.5.3 stable

System information

Windows 10

Issue description

Font rendering on some nodes breaks under some specific conditions. The white box here is supposed to be a "0"

These are the conditions I had to tweak to get it to break in my mrp, they might not all be necessary to reproduce, this is just how I personally ran into this:
oversampling needs to be enabled
the node needs to live inside a viewport node
the node needs to override the theme of a parent node
the stretch mode needs to be set to expand

Steps to reproduce

launch the MRP and simply resize the window to get the pictured result

Minimal reproduction project (MRP)

OversamplingBug.zip

[Calinou]

Thanks for the report! Consolidating in #76450, as this is due to the same cause.

[ace24713]

Oh it is? I saw that issue, but I wasn't confident it was the same since that was a 4.0 issue and for some reason my issue only crops up when a theme is overridden. But alright.