5. A pass two cameras run reads as one camera’s time

Versions: 0.18.1 and 0.19.1.

Each camera runs its own main_opaque_pass_3d, tonemapping and so on, and records its diagnostics span under the same name. The render diagnostics keep one measurement per name per frame, and the smoothing weighs a measurement by the time since the previous one, so with two cameras the reading is whichever camera reported first (or a mix), not their sum.

repros/shadow-cameras --shadows hi --shape sphere, the main_opaque_pass_3d GPU time:

	one camera	two cameras
0.18.1	2.23, 2.71 ms	1.42, 1.21 ms
0.19.1	1.91, 1.68 ms	0.90, 0.90 ms

The second camera draws one small cube, so the true sum is a little above the one-camera figure; the reading halves instead. The same goes for every pass both cameras run, the shadow cascades included (each camera has its own set under the same names).