Always use seamless transition flag when capturing a transition

All transitions capture a screenshot, parent it above everything else in
its container, then orphans the layer once the container has finished
applying its transactions to complete the transition. That is, by
definition, a seamless transition.

This is important for HDR, as previously the seamless transition flag
was NOT used, which was causing tonemapping into SDR rather than
capturing display-relative pixels. Then, if HDR layers were captured,
we'd disable SDR dimming when displaying the screenshot, which
effectively inverse-tonemapped the screenshot into HDR, which caused a
flashing effect.

Bug: 383512175
Flag: EXEMPT bug fix
Test: Circle to Search an HDR video
Change-Id: I04a0828caea2daf293d838c5a03a109822c0bdda