Framebuffer picker size automatically adjusts to match the dimensions of the engine's canvas

[JujieX]

Is your feature request related to a problem? Please describe.
The framebuffer picker's size is dynamically configured to maintain a consistent ratio relative to the engine's canvas dimensions. For example, if the desired ratio is one-half, the render target size of the framebuffer picker will automatically resize to be half the size of the canvas, rather than being locked to a fixed size.