* feat: Add start_updater_thread to update off the main thread
This makes it so that clients can easily not block when wanting to
queue an update.
I have a separate patch which updates the Engine to use this new
API.
I also needed to split the concept of the "next_boot" patch
from the "current_boot" patch, previously refered to as
"current" or "active" patch. This required adding a
report_launch_start api to let the updater library know
when to set current_boot patch from next_boot.
I also removed the rust updater/cli in this as well as the
vmpath argument to init.
I also exposed the report_launch_success api, but its not yet
used by the Engine.
I renamed report_failed_launch to report_launch_failure to match
report_launch_start which I introduced.
* Update naming per comments from Felix.
Also added a helper for char* allocation (not sure if it's better).
* Update library/src/updater.rs
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Co-authored-by: Felix Angelov <felix@shorebird.dev>
Eric Seidel