draft of refactor to make custom confirm modal work for upload; need to further edit sb-file-uploader

Add support for custom confirm modal to sb-file-uploader

Show custom confirm modal when confirming project upload

got custom upload refactor of file upload working, and tested failure case

cleaned up debug code, make project file upload work

simplified logic around canceling file upload

removed old sb-file-uploader.jsx; fixed linter errors

reverted two components to use old strings, not shared

(can do that refactor another time)

removed unnecessary confirm container

removed stray comment

moved, updated sb file uploader tests, related project state tests

removed custom modal, to reduce scope of changes

sb file uploader test uses intl

This fixes the root cause of #2858, which is caused because we are rendering the sound editor based on the GUI editing target data, but retrieving the sound based on the vms editing target data. The throttle of the redux action was causing those to get out of sync while a project was running.

The throttle is not needed because the vm runtime already batches those updates at 30 fps. The updates that come from top-level actions like switching sprites go out immediately.

This is also a minor performance boost, because there was a few ms being spent in setting and checking timers that were not needed.

https://github.com/LLK/scratch-gui/pull/4312 had a function name conflict with the existing code. This change fixes that by renaming the conflicting function, and removes redundant code.

www needs to know when a project finishes loading so that remixing can be disabled while the project is in a state that cannot be remixed.

The playground now displays this on startup when in Scratch Desktop
simulation mode.

Liked @paulkaplan’s suggestion that the property get renamed `showBranding` as we use ‘embedded’ in multiple ways that would get confusing.

The embedded project view is ‘playerOnly’, ‘fullscreen’ and ‘showBranding’.

use blue creating screen for new projects; revised alert text for copy, remix; saving messages don't dismiss alerts

I do not like how the alert component is hyper specialized for two distinct use cases. It would be much better to refactor the alerts so that the alerter can just fill the alert with whatever they want. But I do not feel comfortable making that refactor because I know ben and evelyn have gone back and forth about these alerts.

Listen to the new project changed event from the VM and keep track of the state in Redux.  Update it as appropriate.

Known issue is that the project is marked as "changed" immediately after it's loaded. This is due to asynchronous event emitting while the project data is loaded, and needs an update to the VM to fix.