avm2: Throw error in Loader.unload stub

core: use ctrl+alt+f to dump DO render tree

swf: Merge `read_color_transform_no_alpha` into `read_color_transform`

Differentiate between the cases using a new `has_alpha` boolean
parameter.

tests: Adjust function_base_clip_removed test

Add test for ruffle-rs#5645.

address review comments

ci: Allow manual dispatch of release_nightly workflow

Ignore activity check when release_nightly is manually dispatched.

tests: Expand bitmap_data

core: Changes from review