* Remove usage of HandlerList and reduce usage of Handler.Collection
"The best part is no part" - Elon Musk!
The overwhelming usage of `HandlerList` and `Handler.Collection` was for adding the `DefaultHandler` after the main handler. This PR adds a getter/setter for a `DefaultHandler` on the server, so we no longer need to always create a `Handler.Collection` structure. This has allowed the deprecated `HandlerList` and `HandlerWrapper` classes to be removed.
In implementing this PR, several problems were found in the calculation of `InvocationType`, not least that it was assumed that an empty `Handler.Collection` was `BLOCKING`. When this issue was fixed, any dynamic addition of contexts (deployer or SPI server) failed as the `InvocationType` changed. So this PR also introduces the `isDynamic()` attribute of all `Handler.Container`s. A dynamic container will always return `BLOCKING` from `getInvocationType()`, as there is always a race with a new handler being added. A non-dynamic container will return a real `InvocationType`, calculated from its children, but it's mutator methods will ISE if contained handlers are changed.
Signed-off-by: Simone Bordet <simone.bordet@gmail.com>
Co-authored-by: Jan Bartel <janb@webtide.com>
Co-authored-by: Simone Bordet <simone.bordet@gmail.com>
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