Profiling shows that a considerable amount of time is spent in
glBindBuffer and glBufferSubData when the damage rects are updated.
Since the amount of data here is quite small it's far faster to check if
it's different then to just blindly overwrite the buffer on each call.
Profiled on an Intel CPU with UHD P630 Graphics using magic-trace
This mesh will later be used to render only damaged portions of the desktop.
We also moved the coordinate transformation for damage overlay into a matrix
and computed by the shader.
