Update terminology used in metadata manager

[mProjectsCode]

Some terminology should be updated, e.g. pendingInternalChange to dirty, cyclesSinceInternalChange could become externalWriteLock counting down, with 0 being not locked.

[mProjectsCode]

inactive and subscriptions.length === 0 are identical, so inactive can go.

[mProjectsCode]

In this change, I should also move some logic from the constructor of AbstractInputField to the onMount function

[mProjectsCode]

Maybe also make BindTarget a class and move the logic for subscribing to the metadata manager there. Or put that into the MetadataSubscription. Then make an interface for this and expose it via the API, so that people can use the API to create their own input fields independent of the metadata manager.