This commit fixes two issues with subroots:
1. creating a subroot create a new component node synchronously. This
would causes issues if the creation was done in the setup of a
component, since in that case, owl would reset the current component to
null right after, which would cause all calls to hooks to fail. This is
fixed by restoring the previous component node right after creating a
root.
2. the destroy method for roots calls the scheduler processTasks.
However, the processTasks method was not safe to reentrant calls,
which would in some cases crashes owl. For example, if a destroy is done
while a new component is mounted, the mount method would be called
twice.
This is fixed by ignoring the processTasks if we are currently
processing tasks. It works because the "for ... of" loop will still
process all new tasks in the current iteration.
In this commit, we extend the owl App class to support multiple sub
roots. This is useful for situations where we want to mount sub
components in non-managed DOM. This is exactly what the Knowledge app is
doing, with mounting views in an html editor.
Currently, this requires some difficult and fragile hacks, and still,
the result is that it is very easy to mix components from the main App
and a SubApp. But Knowledge does not actually care about creating a sub
app. It only needs the possibility to mount sub components in dynamic
places.
closes#1640
Géry Debongnie