fix redisplaying figures on same screen

[SimonDanisch]

The following would retain previously scene objects:

using GLMakie
GLMakie.activate!(float=true)

screen = GLMakie.Screen(; size=(600, 450))

f1 = Figure()
Axis(f1[1, 1])
display(screen, f1)

sleep(3)

f2 = Figure()
Axis3(f2[1, 1])
display(screen, f2)

display(screen, Figure().scene)

This PR fixes it!

[MakieBot]

Compile Times benchmark

Note, that these numbers may fluctuate on the CI servers, so take them with a grain of salt. All benchmark results are based on the mean time and negative percent mean faster than the base branch. Note, that GLMakie + WGLMakie run on an emulated GPU, so the runtime benchmark is much slower. Results are from running:

using_time = @ctime using Backend
# Compile time
create_time = @ctime fig = scatter(1:4; color=1:4, colormap=:turbo, markersize=20, visible=true)
display_time = @ctime Makie.colorbuffer(display(fig))
# Runtime
create_time = @benchmark fig = scatter(1:4; color=1:4, colormap=:turbo, markersize=20, visible=true)
display_time = @benchmark Makie.colorbuffer(fig)

	using	create	display	create	display
GLMakie	3.44s (3.43, 3.47) 0.02+-	362.46ms (309.55, 387.01) 35.43+-	465.60ms (460.89, 470.90) 3.41+-	7.12ms (7.05, 7.17) 0.04+-	25.41ms (25.36, 25.47) 0.04+-
master	3.43s (3.41, 3.47) 0.02+-	390.07ms (384.32, 397.44) 5.58+-	474.11ms (465.02, 513.14) 17.28+-	7.12ms (7.01, 7.22) 0.07+-	25.42ms (25.33, 25.58) 0.08+-
evaluation	1.00x invariant, 0.01s (0.54d, 0.33p, 0.02std)	1.08x noisy🤷‍♀️, -27.61ms (-1.09d, 0.09p, 20.51std)	1.02x invariant, -8.51ms (-0.68d, 0.25p, 10.35std)	1.00x invariant, 0.0ms (0.04d, 0.94p, 0.06std)	1.00x invariant, -0.02ms (-0.25d, 0.66p, 0.06std)
CairoMakie	3.05s (3.03, 3.08) 0.02+-	322.01ms (317.61, 328.32) 4.07+-	141.11ms (139.05, 143.82) 1.78+-	7.26ms (7.19, 7.37) 0.06+-	602.87μs (597.09, 609.53) 3.92+-
master	3.08s (3.02, 3.26) 0.08+-	326.72ms (315.90, 356.12) 13.67+-	143.77ms (138.54, 153.98) 6.44+-	7.35ms (7.20, 7.54) 0.12+-	603.89μs (600.22, 609.61) 3.16+-
evaluation	1.01x invariant, -0.03s (-0.51d, 0.37p, 0.05std)	1.01x invariant, -4.71ms (-0.47d, 0.41p, 8.87std)	1.02x invariant, -2.65ms (-0.56d, 0.33p, 4.11std)	1.01x invariant, -0.09ms (-0.94d, 0.11p, 0.09std)	1.00x invariant, -1.02μs (-0.28d, 0.60p, 3.54std)
WGLMakie	3.91s (3.87, 3.95) 0.03+-	360.69ms (353.85, 370.44) 6.07+-	9.68s (9.60, 9.79) 0.07+-	10.59ms (9.72, 14.06) 1.54+-	69.59ms (68.92, 71.48) 0.88+-
master	3.93s (3.87, 3.97) 0.04+-	353.44ms (340.50, 362.35) 7.81+-	9.67s (9.50, 9.80) 0.10+-	9.96ms (9.71, 10.34) 0.23+-	69.88ms (68.42, 71.66) 1.09+-
evaluation	1.00x invariant, -0.01s (-0.40d, 0.47p, 0.03std)	0.98x invariant, 7.26ms (1.04d, 0.08p, 6.94std)	1.00x invariant, 0.01s (0.09d, 0.87p, 0.08std)	0.94x noisy🤷‍♀️, 0.63ms (0.57d, 0.32p, 0.88std)	1.00x invariant, -0.29ms (-0.29d, 0.59p, 0.98std)

[jkrumbiegel]

can confirm that this fixed the mwe on my mac