desktop-shell: Set 1x1 buffers for solid-color backgrounds

When we are going to set a solid color for the background, use
a 1x1 buffer and set the viewport to the full size. This avoids
un-necessary allocation of buffer memory.

Signed-off-by: Harish Krupo <harish.krupo.kps@intel.com>
2 jobs for bg_color_1x1 in 4 minutes and 15 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
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passed #121835
build-native-autotools

00:04:15

passed #121836
build-native-meson

00:02:51