lab_img.theme member was referenced by "modifier" functions when drawing a
hover effect on button buffers or rounding the button buffer for corner
buttons, but this can be prone to use-after-free and was not very clean
because theme and lab_img were referencing each other.
Instead, let's just reference rc.theme in the modifier functions and
remove theme from lab_img.
- fix that icons for normal/hovered/rounded buttons are not placed
exactly the same position
- fix blurry window button icons in scaled outputs
This commit introduces lab_img and scaled_img_buffer and uses them for
rendering icons in the window titlebar. Now the process of rendering
button icons are split into 2 phases: loading with lab_img_load() and
creating scene-nodes for them with scaled_img_buffer_create(). This
might incur some additional overhead since we no longer preload icon
textures, but the rendering of icon only happens for the first window
as backing buffers are shared and the overhead won't be noticeable.
This commit also simplifies the process of centering icon buffer in the
button, by creating icon buffers in a fixed geometry via
lab_img_render().
