Blender Git Loki

Sequencer: fix for the fix of: #23318
also known as: broken multicam strip caused by other fix.

Calculated render_size where it belongs (within the glow effect) and
restored old functionality.

also: renamed render_size to preview_render_size at all relevant places,
where the naming wasn't used correctly.

Hopefully it's now a little bit more clear.

render_size := render size from scene (just rescales width/height)
preview_render_size := preview render size from sequencer preview,
controls the resolution and the use of sequencer proxy sources